III. Calculated PRA (CPRA): The New Measure of Sensitization for Transplant Candidates
During your study in the fellowship program, we will come across the PRA (panel reacting antibodies) and cPRA (calculated panel reacting antibodies). In the UK, it is called cRF (calculated reaction frequency). Please read this article carefully (feel free to use other sources) and address the following:
-
- What is the PRA and how it is calculated?
- What is the difference between PRA cPRA (cRF)?
- How does sensitization affect transplantation?
1- PRA is the test that is done to detect antibodies in recepients sera that can reacts against donor HLA antigens
It is done by mixing patient sera with a pool of lymphocytes from multiple donors
It is also important in determining the degree of sensitization of the recepient ,better to be zero %
>20%needs desensitization , >80% carries a high risk of graft rejection.
If it is high so cross match will be positive
2-In some patients PRA can be high but with negative cross match that’s why the need for the term cPRA or calculated PRA which focuses only on unacceptable HLA antigens which should be defined according to each country .and by contribution from laboratories and transplant centers .
This new definitions of cPRA leads to less positivity of cross matching and decrease in the waiting list of deceased donors .
3-sensitization : is the presence of antibodies in recepient sera that reacts with the donor antigens (graft) leading to hyperactive ,accelerated and acute rejection, delayed graft function and long term complications post transplant caused by:
Pregnancy
Previous blood transfusion
Previous transplantation
What is the PRA and how it is calculated?
Panel reactive antibody is the percentage of a pool of donors to which a recipient had reactive antibodies .the recipient serum is tested against lymphocytes obtained from a panel of about 100 blood donors .A recipient with 80% PRA would be cross match incompatible with 80% of donors .
What is the difference between PRA cPRA (cRF)?
The calculated CPRA is based upon unacceptable HLA antigens to which the recipient has been sensitized and which, if present in a donor , wound represent an unacceptable risk for the candidate or the transplant program . The un acceptable antigens can be identified by the presence of HLA antibodies in the sera of transplant recipients. Like PRA ,CPRA is a tool for characterizing and monitoring sensitization . Unlike PRA, the CPRA provides a meaningful estimate of translatability for most of patients, because it is calculated from un acceptable HLA antigens that will preclude offers from predictably cross match incompatible donors.
.How does sensitization affect transplantation?
Recipients who have preformed antibodies against HLA are at risk for hyper acute rejection , accelerated acute rejection ,antibody mediated rejection ,delayed graft function and longer term complications when transplanted from donor expressing the target HLA antigen .
Sensitized transplant candidates have limited access to transplantation in proportion to how broadly their anti-HLA antibodies react with potential donor population.
Panel reactive antibody (PRA)
It is the percentage of the amount of antibodies in the serum of the patient against donor cells pool . in the population
A score of more than 80 % indicates that the recipient is sensitized.
The calculated CPRA
is based upon unacceptable HLA antigens to which the patient has been sensitized .
The terms “calculated HLA antibody reaction frequency” (cRF) and “calculated panel reactive antibodies” (cPRA) are used synonymously to describe the level of allosensitization, where 0% cRF is nonsensitized, 50% cRF is antibody incompatible with half of a random donor pool, and 90% cRF would be antibody incompatible with 9 out of 10 random donors.
HLA mismatches from a previous transplant and mismatched after pregnancy may considered unacceptable.
cPRA provides a more accurate estimate of sensitization because it includes both class I and class II HLA specificities ..
traditional PRA value meant a high probability of a positive crossmatch
high cPRA value should mean a high probability of a negative crossmatch
Patients who have performed antibodies against HLA antigens are at risk for hyperacute rejection, accelerated acute rejection, antibody-mediated rejection, delayed graft function, and longer-term complications when transplanted from a donor expressing the target HLA antigens.
PRA :
c PRA :
Sensitization:
Unacceptable antigens:
1-PRA Panel Reactive AB
AB in recipient react with panel of normal blood donors pool
calculated with solid phase test
2-cPRA represent actual organ donors that express one or more unacceptable HLA AG
so PRA may be high but cPRA may be less
3-senstization increase risk of hyperacute rejection or at least risk of acut rejection and formation of DSA
regarding the use of the calculated PRA for sensitized candidate for kidney transplantation as it’s recently used calculator to estimate the percentage of donor unacceptable antigenes [UA] for a recipient . This type of calculation will help for better communication with sensitized transplant candidates in waiting list and improve the efficiency of allocation for DD program by reducing unexpected postive cross matches
It’s provided by organ procurement and transplant network (OPTN)in 2009 (1).
The cPRA was developed with complete molecular typing for all donors at the HLA -A,B,C,DRB1,DRB3/4/5,DQA1,DQB1,DPA1,DPB1 the prevalence of UA at DQA,DPA and DPB was studied in a sensitized regional population inUS
Few references from Canadian donation program and Taiwan national donation program using CPRA by adding additional UA from wide donor data base reflect their population which help to improve the accuracy of cPRA and enhance better donor allocation .the combination of cPRA with virtual crossmatch May result in more accurate identification of highly sensitized patients in orders to be prioritized for local , regional sharing program
My references
1-HRSA-OPTN .cPRA calculator .{cited2014jan1
2- up to date
3- American Jornal of transplant 2015;15:3194-3201WileypedriodicalsInc.
the principles of HLA typing for sold organ transplantation we need low resolution typing
Earlier HLA typing was performed by serologic based assay by using cell based cytotoxicity assay which depend on testing the recipient sera against a panel of donors to identify the antiHLA antibodies against donor antigens this method lacking the specificity especially in sensitized recipients it’s not accurate enough to determine the PRA so with improvement in the technology of screening Now we move from serology based screening methods to DNA based molecular and genetic assays which is more specific and sensitive. In determining a wide spectrum of antiHLA AB from wide donor panel that should be representative of the most common phenotypes beads by using solid phase assay like single bead antigen. With this. Technology we able to identify anti HLA AB with high sensitivity and specificity than cytotoxic assay for identifying wide range of class1 HLA molecules and class11 at the level of epitopes
AB that react against. All loci except for DPA can be listed as unacceptable antigen this is very useful. For DD organ allocation program and have been used in USA since 2009 it help in shorting the waiting list for transplantation by finding better matched donors with this technique we
need standardization of the SAB testing with the use of MFI Cutoff positive Value among laboratories Taking in consideration the population diversity
Flow cytometry crossmatch is different from CDC crossmatch its more sensitive to identify igG DSA by using recipient sera added to the donor lymphocytes followed by the addition of flourochrome conjugated AB that detect human IgG
no need to separate T , B cells
the results read out in Quantitative assay as unit of median flouresence intensity MFI the results of flow cytometry
It’s subjective to variability as it depend on the cytometer and it’s setting for each individual lab
So we should keep in mind that flow cytometry crossmatch protocols still not standardized in their testing or reporting
So it’s subjective to false negative and false due to non ALH antigen.ab and presence of IgM antibodies keeping in mind not all IgM AB are benign still those with antiHLA. Specificity can lead to hyper acute or accelerated rejection
Using virtual crossmatch which refers to the use of the results of two actual laboratory tests the antiHLA screening and the HLA type of the donor to decide what of the result is actual crossmatch by using predictive. Positive or negative value in general. Virtual crossmatch have. Mrs than 85% postive predictive value and only 50% negative predictive value
absence of details profile of the patient HLA AB and or insufficient donor HLA typing Can also lead to inaccurate virtual crossmatch assay .
Also regarding SAB assay knowing the shared epitopes is consider essential for proper interpretation of SAB test
panel-reactive antibody (PRA) is a group of antibodies in a test serum that are reactive against any of several known specific antigens in a panel of test cells or purified HLA antigens from cells. It is an immunologic test routinely performed by clinical laboratories on the blood of people awaiting organ transplantation. In this test recipient cells are exposed to random cells of donor population and estimation risk of acute rejection. The PRA score is expressed as a percentage between 0% and 100%. It represents the proportion of the population to which the person being tested will react via pre-existing antibodies against human cell surface antigens, which include human leukocyte antigen|HLA] and other polymorphic antigen systems. A PRA score greater than 6 is in danger, and over 20 requires a desensitization process, but its intensity varies. These antibodies target the surface antigens of target cells, such as HLAs. In other words, it is a test of the degree of alloimmunity in a graft recipient and thus a test that quantifies the risk of transplant rejection. Each population has a different demographic prevalence of particular antigens, so the PRA test panel constituents differ from country to country.
A traditional PRA test is performed using a panel of lymphocytes from potential donor population. Since late 1990s, a purified HLA antigen panel has been used to replace a cell panel for the PRA test, based on the assumption that HLA is the major target antigen system of alloantibody reaction. However, the non-HLA antibody effect on the PRA test has been ignored. (ref:Human leukocyte antigen antibodies for monitoring transplant patients.
CpRA..is the computerised form of traditional PRA ..
It is more accurate and now replaced old PRA in most centers in US it uses more than 120000 donor samples .
Sensitization is a barrier to transplantation and make rejection inevitable if highly sensitised more than 80 % .. it may be antibody mediated or delayed graft function or hyper acute graft rejection .
CPRA represent the unacceptable antigen to which the patient is sensitized which is if present in the donor will be an unacceptable risk to the donor and she will not offered the donated organ for transplant.
CPRA is calculated from HLA antigen frequency of 12000 pooled donors(1).
Difference between. PRA and CPRA:
PRA :
Indicator of general non-specific reactivity
between recipient and potential sample of donor
Measures class-I and class-II antibodies separately
High PRA indicates high probability of positive
crossmatch with a donor offer
Variation in PRA based on laboratory and time of testing.
CPRA :
Calculates specific unacceptable antigens
in the wide donor database
Class-I and class-II both calculated together
Even with a high CPRA, high probability of a
negative crossmatch once the organ is offered
No variation as it is based on a uniform database
Highly sensitized patient will either wait for another donor who has negative cross match or participate in paired donor exchange program or desensitization offer to her.
Reference:
1-Douglas S. Keithand Gayle M. Vranic,Approach to the Highly Sensitized Kidney Transplant Candidate. Clin J Am Soc Nephrol. 2016 Apr 7; 11(4): 684–693.
Around 30% of patients waiting for kidney transplant are said to be considered
sensitized, defined as a panel-reactive antibody (PRA) of 30%–80%(1).
Sensitization is associated with both risk of graft loss and antibody mediated rejection.
Patients with high anti-HLA donor-specific alloantibodies have a relative contraindication
to transplant, in addition to prolong waiting time in organ allocation system. (2)
Still if patient also have positive cross math option will be either:
Wait for another donor who has a negative cross-match, participate in a donor exchange
program or undergo the desensitization process.
Probability of finding a match decreases by:
• Grade of sensitization (PRA) and HLA-antibody profile
• Blood-group
• Geographic location and size of donor pool and time.
Probability of finding a match Increases by:
• Access to living donor and desensitization programs
• Access to living donor
Paired donation programs
• Access to priority programs,
PRA :
Test patient formed HLA antibody ,where patient serum incubate with donor
lymphocytes , obtained from a panel of about 100 blood donors. Percent PRA is the
number of reactions within that panel. If a recipient serum does not react with any of the
donor samples, the candidate is not sensitized and has a PRA of 0. If a candidate’s
serum reacts in 80 out of 100 samples, the patient has a PRA of 80%., means there’s
chance of acute rejection 8 out of 10 times.
CPRA:
Calculation of probability that the recipient and donor would be incompatible.
The system will calculate the CPRA using the unacceptable values that have been
entered for the recipient . To determine the CPRA value, the computer system will use an
established formula and HLA frequencies derived from the HLA types found in more than
12,000 donors.
References:
1- Kim I, VO A, Jordan S, Transplantation in highly HLA-sensitized patients:
challenges and Solutions: Dovepress, 26 Sep.2014 volume2014:6 page 99-107.
2- j.N CecKa,Calculated PRA (CPRA): The New Measure of Sensitization for Transplant
Candidates ican Journal of Transplantation 2010; 10: 26–29.
PRA was simply the percentage of this pool of donors to which a patient had reactive antibodies. A patient with 80% PRA would be crossmatch incompatible with 80% of donors.
PRAIndicator of general non-specific reactivity
between recipient and potential sample of donors while cPRS
Calculates specific unacceptable antigens
in the wide donor database
Sensitization occurs when the recipient is exposed to foreign HLA antigens. In general, sensitization is the result of blood transfusion, pregnancy and previous organ transplantation. Sensitization to HLA antigens has been shown to lead to longer waitlist times and increased death on the waiting list . Furthermore, sensitized patients have increased rates of both antibody-mediated rejection and acute cellular rejection, as well as increased rates of graft loss . Even low-level sensitization with HLA-specific antibodies has been associated with inferior graft outcomes
Sensitization is of of the main barrier to transplantation.sensitized Patients who have preformed antibodies against HLA antigens are at risk for hyperacute rejection, accelerated acute rejection, antibody-mediated rejection, delayed graft function and longer term complications when transplanted from a donor expressing the target HLA antigens.
PRA is the percentage of donors to which a patient had preformed antibodies it’s done by testing patient serum against lymphocytes (WBCs) in a panel of around 100 donor to detect anti HLA antibody, to detect sensitized patient …if negative test with no reaction in the panel this means that patient has no anti HLA antibody with excellent graft prognostic outcome.
A patient with 80% PRA would be crossmatch incompatible with 80% of donors.
solid phase technology is better and it allows the identification of anti HLA Ab with more sensitivity and specificity, the use of single antigen bead assay helped to determine HLA antigens against which recipient Ab is directed.
cPRA is based upon the detection of unacceptable antigens to which the patient has preformed antibodies using donor pool contains 10,000 samples .
Flow cytometry beed assay is used to determine preformed DSA, patient serum is tested against HLA antigens attached to solid beeds , usually multiple antigen FCM beed assay is done to screen for DSA, if positive single antigen beed assay (luminex)-SAB is performed to detect specific HLA antigens to which patient has antibodies.
unacceptable antigens, these are donor antigens that if recipient has antibodies against them, this donor should be excluded because of increased risk of ABMR, different threshold were put to define unacceptable antigens, At one center unacceptable antigen is defined if it has mfi of ≥ 15.000.
Every centre determine its level of unacceptable MFI based on its experience .
PRA :
PRA detects preformed anti HLA antibodies using a panel of typing cell (separate T and B cell panels ) against normal individuals representative of local donor pool and expressed as percentge of panel cells that are killed by the serum .normally 100 cell panel used . .Thus on a 100 cell panel , positive reaction against 65 donors represents a PRA of 65%. It provides the probability of positive crossmatch donors .
Difference between CPRA and PRA :
cPRA (calculated PRA) more consistent and accountible than PRA , computed from HLA antigen frequencies among 12000 kidney donors based on unacceptable class I and II HLA antigens listed for each candidate and represenrs actual percentage of donors with unaccepatble antigens .so higher the cPRA, lesser the transplant offer , so prevents unacceptable transplant offers.
Also ,cPRA includes both class I and II HLA specificities in calculation , so increasing the accuracy of sensitization estimation as compared to PRA which uses different B and cell panels.
PRA accurate measure of sensitizaion wheras cPRA provides meaningful estimate of transplantability
How does sensitization affects transplantation ?
Sensitized patient is the recipient with preformed anti HLA antibodies which remains poential barier to transplantation owing the high risk of hyperacute /accelerated acute and ABMR risk when transplanted from a donor expressing the target HLA antigen.
broadly sentisitized have limited access to transplantation based on the extent of anti HLA Ab.
prior knowledge of sensitization helps in better preparation and planning / search for better compatible donors and avoiding unacceptable donors, utililising densensitization protocols judiciously /priority listing etc.
A kidney transplant is the best available treatment for ESRD because it offers improved quality of life and survival. However, the inadequacy of kidney donors and sensitization to HLAs represent major challenges against transplantation. So every effort is needed to attack these factors.
Pre-transplant patients and donors underwent tough investigations in order to get the most favorable outcome.
Sensitization:
In patients waiting for a transplant, the presence of HLA-specific antibodies against donor antigen prevents transplantation.
Both the degree of sensitivity and the specificity of the antibodies are important. Because the presence of nonspecific antibodies may not affect the transplant outcome.
Cell-based methods to detect the presence of DSA antibodies are:
1-Panel Reactive Antibodies (PRA) test: it is a screening diagnostic test and should not be the sole basis of the decision to proceed with transplantation. It measures the sensitivity of the recipient to the donor HLA antigen, thereby giving clues to the probability of finding a compatible donor. Use pools from the general population.
It is done by a Cell-based cytotoxicity assay mixing the recipient’s serum with donor lymphocytes and complement. Positive reaction means donor cell death, so the recipient is sensitive to DSA by a percent that is calculated by the numbers of positive pools divided by total numbers of pools multiply by 100.
With a high PRA level, the chance to get a suitable donor is reduced, there is an inverse relationship between the PRA level and the probability of receiving a deceased donor kidney transplant.
2- Flow-Cytometry Cross-match(FCXM):
It is the most sensitive method to detect DSA antibodies. In most of the transplant centers and paired kidney exchanges programs, it is considered to be the gold-standard method to determine Donor-Recipient compatibility. Although; it has limitations like:
1- it cannot distinguish HLA from non-HLA antibodies, so can give a false-positive result.
2- It is not universally standardized and the cut-point to define a positive FCXM can be difficult to determine and may vary between laboratories.
in order to decrease the number of sensitized patients on the waiting list for a DD KT new strategies have been developed which include c PRA
Calculated Panel Reaction Antibodies (c-PRA) is virtual crossmatch VXM used to identify (specify) and semi-quantify (strength) the HLA antibodies, performed using solid-phase immunoassays (SPI), which is an evolving technology that may sometimes so sensitive, detecting low levels of DSA that are not clinically significant. It can predict the results of cell-based compatibility assays and it is more sensitive than it. It decreases the waiting time for Recipients for DD.
It uses pools of kidney donors of 12000
If DD kidney available, the top 10 patients on the waiting list underwent VXM by the most recent serum sample;
If VXM + (ie DSA present) and recipient excluded. And
If VXM was negative, update VXM using current serum, and final FCXM done.
Sensitization is more in patients who receive a blood transfusion, previous transplanted, pregnancy. The degree of sensitization affects the induction therapy decision. Plasmapheresis is used for desensitization.
References:
1. Johnson CP, Schiller JJ, Zhu YR. Renal Transplantation With Final Allocation Based on the Virtual Crossmatch.
2. Duquesnoy RJ, Marrari M. Multilaboratory evaluation of serum analysis for HLA antibody and crossmatch reactivity by lymphocytotoxicity methods. Arch Pathol Lab Med. 2003 Feb;127(2):149–56.
3. Edition S. Handbook of Kidney.
Dear All
Thank you for your replies. Feel free to contribute to the discussion for those who did not. Also, let us not forget week 2.
Patients who have preformed antibodies against HLA antigens are at risk for hyperacute rejection, accelerated acute rejection, antibody-mediated rejection, delayed graft function and longer term complications when transplanted from a donor expressing the target HLA antigens.
The circulating anti-HLA class I antibodies bind to the expressed antigens on endothelial cells resulting in complement activation and cell
death. This in turn attracts different immune cells ,such as granulocytes and
platelets and the formation of microthrombi and necrosis.
Priming of the immune response to HLA class I and / or II can occur as a result of pregnancy, blood transfusions or rejection of a previous transplant. However, there are
individuals who have HLA antibodies with no history of exposure to the above
factors.
PRA has been the measure of sensitization. Panel reactive antibodies (PRA) simply the percentage of the donors pool to which a patient had reactive antibodies. The test done by mixing a patient’s blood (serum) against lymphocytes (white blood cells) obtained from a panel of about 100 blood donors. These 100 donors represent the potential HLA makeup for a donor from that area. A patient with 80% PRA would be crossmatch incompatible with 80% of donors.
The CPRA represents the percentage of actual organ donors that express one or more of the unacceptable HLA antigens. Entering an unacceptable antigen for a patient means that kidneys from donors expressing that antigen will not be offered for
that patient. The higher the CPRA, the fewer offers would be received.
Dear All
Thank you for your replies. Feel free to contribute to the discussion for those who did not. Also, let us not forget week 2.
Around 30 percent transplant recipient have antibodies HLA [1],
sensitization from prior exposures to HLA antigens, such as pregnancies, blood transfusions, and previous transplantation.
PRA is group of immunological test done to assess transplant recipient for evidence of immunization to different antigen in population ,those with highly sensitized will have more risk of rejection ,delayed graft function and more other complication.
It’s the percentage of population of donors to which recipient will have an antibody, those with 80 % will have an 80% chance of having incompatible cross match.(2.3)
CPRA represent the unacceptable antigen to which the patient is sensitized which is if present in the donor will be an unacceptable risk to the donor and h will not offered the donated organ for transplant.
CPRA is calculated from HLA antigen frequency of 12000 pooled donors (3).
CPRA provide more accurate estimation of sensitaization as it include both claa I and class II .
ASSY IS BY:
Cell-based cytotoxicity assays :
Recipient serum is mixed with donor lymphocytes, along with exogenous complement and a viability dye.(4) If the serum contains antibody capable of binding to the donor cells and fixing complement, cell death occurs.
IF cell death is observed in 45 out of the 60 different cell donors in the panel, the recipient has PRA) of 75 percent and would be ineligible to receive a graft from 75 percent of the donor population on the basis of having preformed DSA that would likely result in a positive cytotoxic crossmatch against these donors.
Solid phase assays:
recipient serum is added to a cocktail of polystyrene beads, to which purified HLA antigens are attached .(5) A fluorochrome-conjugated anti-immunoglobulin G detection antibody is then added, and the presence of anti-HLA IgG isotype antibody is identified by flow cytometric methods (Luminex).
Reference:
1-https://optn.transplant.hrsa.gov/data/request-data/ (Accessed on June 06, 2018).
2- M. Cecka , Calculated PRA (CPRA): The New Measure of Sensitization for Transplant Candidates. American Journal of Transplantation 2010; 10: 26–29.
4-https://optn.transplant.hrsa.gov/media/1200/optn_policies.pdf#nameddest=Policy_07 (Accessed on June 06, 2018).
5-Reed EF, Rao P, Zhang Z, Gebel H et al, Comprehensive assessment and standardization of solid phase multiplex-bead arrays for the detection of antibodies to HLA.. Am J Transplant. 2013;13(7):1859. Epub 2013 Jun 13.
Deleted due to repetition
Ahmed Halawa
Dear Ibrahim
Thank you for your reply, but you copied the same reply in week 2. Your repeated reply will be deleted.
Dear All
It was a good start, but feel free to add more contributions especially those who did not contribute much and did not contribute at all.
thank you sir,
it is already my own writting. the questions are almost the same and my answers are also the same. I didn’t get the difference.
1- PRA is a percentage of reactive anti-bodies to a panel of donors. e.g if PRA is 40 %, it means that this recepient has sensitive antibodies to 40 % of that pool of donors. class I and II HLA specificities are measured separately. calculated PRA is based on an unacceptable HLA antigens that were computed from HLA antigen frequencies in 12,000 kidney donors. it provides more accurate estimate of sensitization as it include both class I and II HLA specificities.
2- cRF is equal to CPRA but the former term is used in UK. it is a measure of sensitization of a recepient to possible donors. if cRF is high, it means high sensitization and less chance of successful transplantation.
3- sensitization adveresly affects the outcome of transplantation, esp. in the 1 st year. it will affect the graft survival, acute rejection rate, degree of immunosuppression and hence higher risk of infections.
III. Calculated PRA (CPRA): The New Measure of Sensitization for Transplant Candidates
During your study in the fellowship program, we will come across the PRA (panel reacting antibodies) and cPRA (calculated panel reacting antibodies). In the UK, it is called cRF (calculated reaction frequency). Please read this article carefully (feel free to uses other sources) and address the following:
1/ What is the PRA and how it is calculated?
PRA is the percentage of this pool of donors to which a patient had reactive antibodies.
A patient with 80% PRA would be crossmatch incompatible with 80% of donors.
PRA is a group of antibodies in a test serum that are reactive against any of several known specific antigens in a panel of test cells or purified HLA antigens from cells.
It is an immunologic test routinely performed by clinical laboratories on the blood of people awaiting organ transplantation.
In this test recipient serum is tested against random cells of donor population and estimation risk of acute rejection.
The PRA score is expressed as a percentage between 0% and 100%. It represents the proportion of the population to which the person being tested will react via pre-existing antibodies against human cell surface antigens, which include HLA and other polymorphic antigen systems.
A PRA score greater than 6 is in danger, and over 20 requires a desensitization process, but its intensity varies. These antibodies target the surface antigens of target cells, such as HLAs. In other words, it is a test of the degree of allo-immunity in a graft recipient and thus a test that quantifies the risk of transplant rejection.
Each population has a different demographic prevalence of particular antigens, so the PRA test panel constituents differ from country to country.
A traditional PRA test is performed using a panel of lymphocytes from potential donor population. Since late 1990s, a purified HLA antigen panel has been used to replace a cell panel for the PRA test, based on the assumption that HLA is the major target antigen system of alloantibody reaction. However, the non-HLA antibody effect on the PRA test has been ignored.
A high PRA value usually means that the individual is primed to react immunologically against a large proportion of the population. Individuals with a high PRA value are often termed “sensitized”, which indicates that they have been exposed to “foreign” proteins in the past and have developed antibodies to them.
These antibodies develop following previous transplants, blood transfusions, infections and pregnancy. Transplanting organs into recipients who are “sensitized” to the organs significantly increases the risk of rejection, resulting in higher immunosuppressant requirement and shorter transplant survival.
People with high PRA scores therefore wait longer for an organ to which they have no pre-existing antibodies.
Extensive efforts have been made to identify treatment regimens to reduce PRA in sensitized transplant candidates.
In certain circumstances, plasma exchange, IVIG, Rituximab and other “antibody-directed” immune therapies may be employed, but this is an area in which active investigation continues.
Reference:
(ref:Human leukocyte antigen antibodies for monitoring transplant patients. Surg Today. 2005;35(8):605-12.)
2/ What is the difference between PRA cPRA (cRF)?
The calculated CPRA is based upon unacceptable HLA antigens to which the patient has been sensitized and which, if present in a donor, would represent an unacceptable risk for the candidate or the transplant program.
The CPRA is computed from HLA antigen frequencies among approximately 12,000 kidney donors in the United States between 2003 and 2005 and thus represents the % of actual organ donors that express one or more of those unacceptable HLA antigens.
What adds accountability is that entering an unacceptable antigen for a patient means that kidneys from donors expressing that antigen will not be offered for that patient.
The higher the CPRA, the fewer offers would be received.
The proposal was approved by the UNOS Board of Directors and the initial phase was implemented in December 2007.
CPRA provides a more accurate estimate of sensitization because it includes both class I and class II HLA specificities in the calculation, a major departure from traditional PRA, where class I and class II specificities are measured separately.
Even B-cell panels, which express both class I and class II antigens are generally constructed to cover the class II HLA antigens and are not representative of HLA distributions in the general population.
Despite these limitations, laboratories can accurately predict many incompatible crossmatches, streamlining allocation and providing more options for broadly sensitized patients. Like PRA, CPRA is a tool for characterizing and monitoring sensitization.
Unlike PRA, the CPRA provides a meaningful estimate of transplantability for most patients, because it is calculated from unacceptable HLA antigens that will preclude offers from predictably crossmatch incompatible donors.
Although the concepts of unacceptable antigens and virtual crossmatches have been with us for many years, their widespread use and formal incorporation into the system for kidney allocation in the United States is unprecedented.
As our ability to predict crossmatches and compatibility of donors for sensitized patients improves, it should be possible to encourage wider geographical sharing of deceased donor kidneys for this disadvantaged group beyond the current practice of sharing zero-HLA mismatched kidneys for sensitized patients.
Accurate crossmatch prediction is a critical aspect of paired living-donor kidney exchanges as these increasingly involve patients and donors at different transplant centers.
Finally, although the current focus is on their role in renal transplant allocation, unacceptable antigens and CPRA are also important tools for many thoracic programs that have begun using virtual crossmatches for distant donors to broaden the opportunities for their sensitized patients.
How does sensitization affect transplantation?
Sensitized patients have limited access to suitable donors depending on their level of antibodies and ability to reduce or remove these antibodies by treatment, if they are transplanted, they will be exposed to higher risk of antibody mediated rejection.
The best options for them either to have desensitization and wait for suitable donor.
How many samples were used for cPRA compared to PRA?
12000
You mentioned, “PRA is a measure used to predict the probability to find a compatible donor for kidney transplantation”. is an accurate measure PRA a measure of transplantability or sensitization?What about the consistency of the PRA results?
Can the PRA differ between labs?
Affected by the population of donors, is different between labs, between countries, depends on centers local policies and protocols.
What is the difference in the size of the panel between PRA and cPRA?
What are the techniques used in both?
Thanks for all the responses. What do you think will make a difference in CPRA between different areas and will affect the definition of sensitization and transplant decision ?
Answered earlier.
Excellent Dr Mohamed
Sensitised patient
-have circulating HLA antibodies that developed after exposed to HLA antigens due to pregnancies, blood transfusions and failed transplantation.
-high risk of hyper acute rejections or of accelerated acute rejection
-presence of preformed HLA antibodies limits the compatible donors.
-sensitised patients often have to wait longer for compatible kidneys
pra-
Since the discovery in the mid-1960s that catastrophic hyperacute rejection was linked to anti-donor HLA antibodies, PRA has been used to assess sensitization. Patel and Terasaki’s seminal study also outlined a simple surrogate test that might identify sensitised patients and assess their chances of finding a crossmatch-compatible donor using a panel of normal blood donors as a proxy for the prospective local organ donor pool. The fraction of this pool of donors to which a patient had reactive antibodies was known as PRA. A patient with an 80 percent PRA level would be incompatible with 80 percent of donors.
cPRA-
The UNOS Histocompatibility Committee devised a proposal to increase PRA reporting accountability while also taking advantage of new and evolving technology. The CPRA is computed using non-acceptable HLA antigens to which the patient has been sensitised and which, if present in a donor, would provide an unacceptable danger to the candidate or the transplant programme. Between 2003 and 2005, the CPRA was calculated using HLA antigen frequencies from roughly 12,000 kidney donors in the United States between 2003 to 2005 and thus reflects the percentage of actual organ donors who express one or more of the HLA antigens that are considered undesirable. The fact that entering an undesirable antigen in the system for a patient will mean that kidneys from donors who express that antigen will not be provided to that patient increases accountability. Less offers would be received if the CPRA was higher.
Due to traditional PRA’s underestimating of the patients’ sensitization levels, concordance was frequently worse among the lower PRA groups. Because it combines both class I and class II HLA specificities in the computation, CPRA provides a more accurate estimate of sensitization than standard PRA, which measures class I and class II specificities individually.
sensitization-
When the recipient is exposed to foreign HLA antigens, he or she becomes sensitised. Sensitization is most commonly caused by blood transfusions, pregnancy, or previous organ transplantation.
Sensitization to HLA antigens has been linked to longer wait periods and an increased risk of dying while on the waiting list . Additionally, sensitised patients had higher rates of antibody-mediated and acute cellular rejection, as well as graft loss . Even low levels of HLA-specific antibody sensitization have been linked to poor transplant outcomes.In patients who are highly sensitised (taken as PRA> 98 percent in this study), evidence suggest that the mechanism of sensitization has an impact on kidney transplant survival. Survival of kidney allografts in the highly sensitised patients is much lower than that of non-sensitized patients.Survival of kidney allografts in severely sensitised patients who have had a re-transplant are much worse off than those who did not receive a re-transplant as a way of sensitising event.
The mode of sensitization and its influence on allograft outcomes
in highly sensitized kidney transplant recipients
Robert R. Redfield1, Joseph R. Scalea1, Tiffany J. Zens1, Didier A. Mandelbrot2, Glen Leverson1,Dixon B. Kaufman1 and Arjang Djamali1,2
cPRA
-implemented by UNNOS in Dec 2007
-to solve the variability in PRA reporting that developed over the time by using different call panels and diff test for HLA antibodies
-calculated by determining the probabilities of incompatible donor HLA phenotypes based on unacceptable class 1 and 2 HLA antigens that has been listed
-shows the true frequencies of an incompatible donor based on unacceptable antigens that has been listed for the patient
-cPRA -80% means 80 percent of deceased donor kidneys will have at least one unacceptable antigens and make the patient not suitable for transplant
-different centres have different threshold for unacceptable antigens
-interpretation of the test before transplantation might not be as easy or straight forward. So, it requires comparing more than one test platforms to assure the weak reactions are similar among the tests.
PRA tests the patient’s serum reaction against a panel of lymphocytes from normal individuals that are representative of the local donor pool.
The result also is an estimate of how often the patient would have a positive crossmatch against available donors. PRA is the first test for measuring sensitization. Methods used to measure sensitization progress over time. CDC was the earliest method. FCXM is very sensitive crossmatch test and solid phase assays are available.
CPRA provides an estimate of percentage of deceased organ donor that will be crossmatch incompatible for a candidate. CPRA is calculated by determining the frequency of incompatible donor HLA phenotypes based upon unacceptable class Ι and class ΙΙ have been listed for each candidate.
since the HLA -A, -B, -DR, -DQ types of actual deceased kidney donors were used to compute to the antigen frequency CPRA reflects the true probability of incompatible donor based on the unacceptable antigens for a patient. A CPRA using national donor pool. A CPRA of 80% means that 80% of deceased donor kidneys will express at least one unacceptable HLA antigen for patient.
High PRA value means a high probability of positive crossmatch, but a high CPRA should mean a high probability for negative cross match.
Sensitization leads to more acute and chronic rejection and correlate with lower graft survival than non-sensitized patients although patient survival compare to patients in waiting list for transplantation is better.
The same patient might have a different CPRA at different transplant center with different thresholds for assigning unacceptable antigens.
-Sensitization is still a serious obstacle to transplantation.
-Sensitization can be caused by past blood transfusions, previous transplants, or pregnancy.
-Patients with a sensitization level of less than 30% should be evaluated for desensitization.
-Desensitization is a technique for lowering anti-HLA antibody levels, allowing for transplantation with a low risk of graft rejection. It is performed by
Plasma exchange, immunoadsorption, rituximab, or intravenous immunoglobulins are all options.
-Hyperacute rejection, increased acute rejection, ABMR, impaired graft function, and long-term problems are all risks for sensitized patients after transplantation.
-PRA is a way for determining a transplant patient’s sensitivity; it refers to the percentage of donors against whom the patient has reactive antibodies.
Mixing recipient blood with a panel of donor lymphocytes is used to determine it.
Patient with PRA of 80% means that the recipient responds to 80% of the available donor.
-cPRA (calculated PRA) is more accurate than PRA since it is based on unacceptable HLA Ags to which the recipient has been sensitized and is recognized an unacceptable risk for the candidate if these Ags are present in a donor.
-When compared to PRA, CPRA is recommended since it uses around 12000 kidney donors’ donor lymphocytes, resulting in a huge pool that represents a significant number of organ donors. In addition, unlike PRA, which measures class I and class II specificities individually, cPRA includes both class I and class II HLA specificities in the final assessment.
-For some patients, antibodies to the HLA-Cw, DQ alpha chain, and DP antigens may impair accurate crossmatch prediction.
panel reacting antibodies (PRA) is testing patient,s serum against a panel of lymphocytes from normal individuals representative of the local donor pool. It is the first measure for sensitization.it represents a positive crossmatch over the total number of donors tested. A high percentage of PRA means is difficult to find a suitable donor.
CPRA is based on class I and II HLA antigens that are listed as unacceptable for the patient.it reflects the probability of an incompatible donor based on unacceptable antigens that have been listed for the patient.
Sensitization can affect transplant :
-Hyperacute rejection.
-Accelerated acute rejection( early and rapid antibody-mediated rejection)
-Restrict the number of compatible donors for the patient.
PRA has been used as a diagnostic marker of sensitization before kidney transplantation. Sensitization is related to preformed anti-HLA antibodies and shows risk of hyperacute or accelerated ABMR rejection in transplants. A transplant candidate with 80% PRA indicates 80% likelihood of positive crossmatch against a regional donor pool and was considered sensitized. However with introduction of more sensitive tests (solid-phase antibody tests) the number of sensitized candidates in waiting list are increased. So UNOS committee decided to use unacceptable antigens for class I and class II HLA. CPRA is calculated by computer program in patient’s geographic region. By determination of donor’s HLA before transplantation, sensitized candidates with high CPRA with negative virtual crossmatch have priority to others.
Thank you all for your contribution. Remember, the summary would be better in 250 words.
Penal reactive antibodies, it is the antibodies to the HLA antigens ; the calculated one it the measurement of antibodies to the most common shared antigens in most populations , it was the old method now the used to do specific antibodies screening for the particular recipient and if it positive the do specification to get the donor specific antibodies.
The more the recipient had antibodies either to this donor (DSA) or not (positive PRA but not DSA ) it affect the graft survival by the complications of heavy immunosuppressive medication or by antibody mediated rejection
III. Calculated PRA (CPRA): The New Measure of Sensitization for Transplant Candidates.
PRA:
A traditional PRA test is performed using a panel of lymphocytes from potential donor population. Since late 1990s, a purified HLA antigen panel has been used to replace a cell panel for the PRA test, based on the assumption that HLA is the major target antigen system of allo-antibody reaction. However, the non-HLA antibody effect on the PRA test has been ignored. (ref:Human leukocyte antigen antibodies for monitoring transplant patients. Surg Today. 2005;35(8):605-12.)
The difference between PRA cPRA (cRF)
Sensitization & transplantation
Patients who have preformed antibodies against HLA antigens are at risk for :
Excellent Assafi
Very impressed with your answer.
Thanks for all the responses. What do you think will make a difference in CPRA between different areas and will affect the definition of sensitization and transplant decision ?
Pre transplantation sensitization is main cause of acute rejection & graft failure. So through pre transplantation assessment , the presence of recipient sensitization can be measured by PRA test.
PRA is defined as the presence of recipient Ab against number of donor HLA Ag ( single or multiple) & it expressed by percentage of the donor expected to have Ag that the recipient is sensitized to it. PRA measure antibodies against either class I or II Ag. It measured by solid-phase technologies. PRA is reflect donor specific risk but not reflect risk of immunologic events after transplantation.
UNOS started using CPRA in 2007 to assess the variability of PRA reporting which developed over years by using a different cell panel & different laboratory test to assess HLA Ab. CPRA is defined by identifying the frequency of incompatible donor HLA Ag (class I & II ) listed for each recipient.
Using of CPRA is became main test in transplant labs worldwide because the result of CPRA is more accurate for recording sensitization than standard PRA.
Sensitization is the barrier of transplantation and patients who have preformed Ab against HLA Ag are considered at higher risk of hyperacute and accelerated acute rejection , Antibody mediated rejection and delayed graft function …..
PRA (Panel Reactive Antibody) is a test used in pre transplant period to evaluate the patient sensitization hence helping to prevent graft loss . It measures the recipient Abs against HLA Ags in candidate donors in the regional pool ….it is done by mixing the the lymphocytes of the candidate donors with recipient serum and calculate what is percentage of the positive reactions.
A recipient with 80% PRA this means that his crossmatch will be incompatible with 80% of donors.
cPRA (calculated PRA) is more accurate than PRA , it is based on unacceptable HLA Ags to which the recipient has been sensitized and if these Ags present in a donor , are considered an unacceptable risk for the candidate.
CPRA is preferred as it uses approximately 12000 kidney donors donor lymphocytes making a large pool which represent a large numbers of organ donors compared to PRA.
Also cPRA involves both class I and class II HLA specificities in the final calculation compared to
PRA that class I and class II specificities are measured separately
PRA : represents the percentage of anti-HLA antibodies against the potential donor from general population that may be directed against HLA class I or/and class II antigens . zero PRa means the recipient has no preformed anti HLA Abs with expected excellent graft survival , while if PRA is 80 % this means the patient has preformed Anti HLA Abs against 80 % of potential donors.
C PRA is more refined PRA form used to detect the percentage of the unacceptable HLA Ags present in the potential donors and it depends on the frequencies of HLA antigens within a particular donor population,
In kidney transplantation , sensitized patients represents a challenge as it is difficult to find a suitable donor to them so they tend to remain on dialysis for longer time than none sensitized ones with all its related complications , also they commonly suffer from many catastrophic complications if receive a kidney from a donor to whom they have preformed Abs .These complications include hyper acute and accelerated acute rejection , delayed graft function , poor graft survival as well as other short and long term complications .
PRA : represents the percentage of anti-HLA antibodies against the potential donor from general population that may be directed against HLA class I or/and class II antigens . zero PRa means the recipient has no preformed anti HLA Abs with expected excellent graft survival , while if PRA is 80 % this means the patient has preformed Anti HLA Abs against 80 % of potential donors.
C PRA is more refined PRA form used to detect the percentage of the unacceptable HLA Ags present in the potential donors and it depends on the frequencies of HLA antigens within a particular donor population.
In kidney transplantation , sensitized patients represents a challenge as it is difficult to find a suitable donor to them so they tend to remain on dialysis for longer time than none sensitized ones with all its related complications , also they commonly suffer from many catastrophic complications if receive a kidney from a donor to whom they have preformed Abs .These complications include hyper acute and accelerated acute rejection , delayed graft function , poor graft survival as well as other short and long term complications .
The panel-reactive antibody (PRA) test is a routine screening measure to assess the degree of a potential kidney recipient’s sensitization.
It is also affecting the optimal choice of immunosuppression protocol, including the type of induction therapy.
It is a complement-fixating assay to test the ability of recipient’s serum to lyse a panel of T-cells from a group of potential donors.
For a PRA of 20%–80%, there is 50% chance to be transplanted compared to nonsensitized patients while the chance is only 5% for PRA greater than 80%.
PRA titre is measured using the complement-dependent cytotoxicity test (PRA-CDC) as a standard procedure
A calculated PRA (cPRA), based on a population’s HLA frequency and patients’ unacceptable antigens (UAs), correctly estimates the percentage of donors suitable for candidates i.e., The cPRA estimates the percentage of donors with whom a particular recipient would be incompatible
The calculated panel reactive antibody (CPRA), which is based upon unacceptable HLA antigens listed on the waitlist form for renal transplant candidates, replaced PRA as the measure of sensitization
The goals of introducing the CPRA were to provide a more consistent and accountable measure of sensitization among kidney transplant candidates. The unacceptable antigens that are listed to generate the CPRA represent a positive ‘virtual’ crossmatch by defining those HLA antigens that would be unacceptable in a donor
The combination of a desensitization protocol (MMF, plasmapheresis and ATG) are effective strategy for sensitized patients awaiting renal transplantation.
***What is the PRA and how it is calculated?
Panel reactive antibody (PRA) detects preformed recipient antibodies using a panel of typing cells and gets a percentage of cells that the serum reacts.
Panel reactive antibodies (PRAs) have been used to measure the relative degree of sensitization in renal allograft recipients. PRA levels represent the percentage of likely cross-match incompatible donors, and are determined by testing recipient sera against cells from a panel of HLA-typed donors or solubilized HLA antigens attached to a solid phase. The panels should be representative of the local pools of potential organ donors. However, the results of PRA testing can be highly variable and inconsistent depending on the panel composition and the techniques used for HLA antibody detection .PRA tests could sometimes determine the HLA target specificities (a list of HLA antigens that react with the patient’s serum) by analyzing reaction patterns against the HLA types of the panel donors.
***What is the difference between PRA cPRA (cRF)?
# PRA ( Panel Reactive Antibody ) tests could sometimes determine the HLA target specificities (a list of HLA antigens that react with the patient’s serum) by analyzing reaction patterns against the HLA types of the panel donors. However, when multiple antibodies are present in a serum, antibodies to more frequent HLA antigens mask the recognition of antibodies to less-frequent antigen.
# calculated panel-reactive antibody (CPRA) is calculated by determining the frequency of incompatible donor HLA phenotypes based on the unacceptable class I and class II HLA antigens that have been listed for each candidate.
Since the HLA-A, -B, -C, -DR, and -DQ types of actual deceased kidney donors were used to compute the antigen frequencies, the CPRA reflects the true probability of an incompatible donor based on the unacceptable antigens that
have been listed for a patient. A CPRA of 80% means that 80% of deceased donor kidneys will express at least one unacceptable HLA antigen and will not be offered to that patient. A CPRA calculated using a national donor pool may
not always reflect the HLA antigen distribution of a local donor population that different regions because they differ in the racial and ethnic composition, but these variations generally do not result in substantially different CPRAs.
We must concentrated that main different issue between PRA and cPRA is that the number of samples more than 12000 compared to less number from the pool of the general population.
***How does sensitization affect transplantation?
More than one-third of patients awaiting a renal transplant in the United States are sensitized to HLA antigens. They have circulating HLA antibodies that developed from exposure to allogeneic HLA antigens during the course of
pregnancies, through exposure to blood transfusions or, increasingly, because of a failed transplant. Patients who have circulating HLA antibodies are at high risk of hyperacute rejection (the immediate and usually irreversible destruction of the transplanted kidney) or of accelerated acute rejection (an early and rapid antibody-mediated rejection that is not easily controlled with immunosuppression). The presence of preformed HLA antibodies restricts the number of compatible donors for the sensitised patient to those who do not express the HLA antigens to which the patient is sensitised. Sensitized patients often must wait substantially longer for a crossmatch compatible kidney. Assiduous attention to pretransplant lymphocyte crossmatching has virtually eliminated hyperacute rejection as a clinical threat. Very sensitive solid-phase antibody tests and the virtual crossmatch make it possible to avoid donor reactive antibodies completely for many patients today even those who are broadly sensitized against many HLA antigens.
-PRA is a test used to identify the presence of antibodies to HLA antigens by adding the patient’s serum to a panel of lymphocytes from multiple donors according to local area .
A 50 % score means that the recipient react with half of the donors , HLA matching of the potential donor is checked for possible reactive antigens.A score of more than 20 % indicates sensitization.
-PRA results may vary from one lab to another
-The calculated PRA is based upon unacceptable HLA antigens to which the patient has been sensitized and would represent an unacceptable risk for the candidate if present in the potential donor.
-CPRA represent the percentage of actual organ donors that express one or more of these unacceptable HLA Antigens among 12,000 kidney donors.
– percentage of the people from general population carring that unacceptable Ag is the CPRA of that patient
-CPRA uses luminex technique hence more specific then PRA in detection and identification of sensitization, it includes both class I and class II HLA specificities in the calculation, a major where class I and class II specificities are measured separately in classic PRA.
-PRA value meant a high chance of a positive crossmatch
-High CPRA value means a high chance of a negative crossmatch
-Patients who are sensitized , various risks must be anticipated , according to the degree of sensitization , and the mean florescence intensity number .Compliacations include rejection hyperaacute or AMR , delayed graft function , and poor graft outcome .
PRA (Panel of reactive antibody):
cPRA (calculated PRA):
Sensitization:
Unacceptable antigens:
1.Panel reactive antibodies (PRA) test is a laboratory immunological test used to screen and detect percentage of sensitization of patient to the potential donors.
There are different techniques of PRA.
☆ Cytotoxic method (classical)
Complement-dependent cytotoxicity (CDC)
• was developed by Terasaki 1964
• the patient serum put to the cell of the different donors in tray to detect the antibodies.
• death of the donor cell in well of the tray is caused by Cytotoxicity due to reactive the recipient antibodies to the donor antigen.
• PRA is calculated by reactive wells number divided by whole wells number. For example 24 reactive well in total 48 wells ,so PRA is 50 %.
• less sensitive method
• it use few number of donor
☆ Current methods
• they replace the cell by beads which coated with HLA molecules.
• there is either multi-antigen beads (flow PRA) or single antigen bead ( Luminex)
• PRA is calculated by dividing number of reactive beads (antibodies attached) by total beads number. For example, in case of 20 % of beads attached to the antibodies, so the PRA is 10%
Score of PRA: 0-100% , where PRA of 10% means sensitized patient , and more than 85% is highly sensitized.
• more sensitive than cytotoxic method.
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2. Calculated PRA (cPRA) is computerized idea of PRA.
• While PRA is a physical crossmatch technique, cPRA is a virtual one.
• Frequncy of HLA antigen from 1200 American kidney donors is used to estimate the cPRA.
• It’s importance is detection of the unacceptable HLA antigen in the actual donors to exclude them from certain sensitized recipient.
• It is more accurate than PRA in recognition of sensitization because cPRA uses both HLA class 1 and 2 in calculation, while PRA measures class 1 and 2 separately.
• Higher value of cPRA means that a NEGATIVE crossmatch is a high probability, while high value of PRA indicates that a POSITIVE crossmatch is a high probability.
Both of them (PRA and cPRA) represent a measure of sensitization, but cPRA alone is a measure of transplantability as it exclude the potential incompatible donors.
————————–
3. Sensitization is a major obstacle for transplantation because the highly sensitized patient has increased risk for graft rejection (hyperacute, acute, antibody-mediated) or delayed graft dysfunction
• Causes of sensitization are previous blood transfusion, previous transplantation or pregnancy.
• Desensitization is used to decrease the level of anti-HLA antibodies to allow transplantation without high risk of graft rejection.
It is done by plasma exchange, immunoadsorption, rituximab or intravenous immunoglobulins.
Thanks Ahmed, well done
PRA is calculated by dividing number of reactive beads (antibodies attached) by total beads number. For example, in case of 20 % of beads attached to the antibodies, so the PRA is 10%{ How 20% becomes PRA 10% please can clarify it to me)
The PRA, which initially predicted the percentage of cross-match incompatible local donors, evolved from its original form to a less meaningful measure of sensitization with the introduction of more sensitive antibody tests and developments in our understanding of HLA antigens.
When the PRA test was first developed, only a few class I HLA antigens had been characterized. As more HLA antigens were identified, the panel compositions were adjusted to include as many different antigens as possible.
Although these changes improved the chances of detecting HLA antibodies directed against any of a broad spectrum of HLA antigens, the correlation between PRA and the probability of a positive crossmatch against potential donors was lost because the frequencies of antigens on the panel had been altered .
The calculated PRA (CPRA) is determined by calculating the probability of incompatible donor HLA phenotypes based on the unacceptable class I and class II HLA antigens that have been provided for each candidate.
The CPRA indicates the genuine chance of an incompatible donor based on the unacceptable antigens that have been indicated for a patient
. A CPRA of 80% indicates that 80% of dead donor kidneys are unsuitable for that patient and will not be provided. Although we could expect varied HLA antigen distributions in various locations due to differences in racial and ethnic groups, preliminary research reveals that these differences do not result in significantly different CPRAs.
PRA results from an immunologic test which is routinely performed on the blood of people awaiting organ transplantation. In this test recipient cells are exposed to random cells of donor population and estimation risk of acute rejection. The PRA score is expressed as a percentage between 0% and 100%.
PRA is the percentage of
donors to which a patient had reactive antibodies. A patient with 80% PRA would
be crossmatch incompatible with 80% of donors.
The calculated CPRA is
based upon unacceptable HLA antigens to which the patient has been sensitized
and which, if present in a donor, would represent an unacceptable risk for the
candidate or the transplant program. The higher the CPRA, the fewer offers
would be received.
Individuals with a
high PRA value indicate that they are sensitized, which indicates that they
are at high risk of graft failure in transplantation.
PRA (Panel Reactive Antibodies) determine whether or not a patient already has any specific HLA antibodies. The obtained blood sample is compared to about 100 samples and the reaction of the samples is calculated. the ratşo is set as PRA. for example if positivity is 70 or 80 out of 100 samples then the recipient has a chance of 70 or 80 % risk of sensitization. cPRA takes into consideration samples from actual donors, not the general population. moreover is takes into account the unacceptable antibodies ented as unacceptable for that specifşc patient. Sensitization affects patients negatively by increasing the risk of rejection necessitating high dose immune suppression and considering recipients as high risky
cPRA has more samples (more than 12000) which make it more informative about risk of sensitization
PRA is widely used for measuring the degree of sensitisation patient with high PRA value > 80% is considered sensitized or positive crossmatch this recognized when reaction occurs between the serum of the recipient and serum of 100 patient.
High PRA cause hyperacute rejection, antibody mediated rejection, delay graft function and also cause long term complications.
CPRA also used to identify sensetization but it differs from PRA by calculating just unacceptable HLA antigens.
sensitization
remains a barrier to transplantation
If the patients have a preformed Abs against HLA Ags ,would be at risk for :
1-hyperacute rejection
2-accelerated acute rejection
3-Antibody-mediated rejection
4-delayed graft function
5- longer term complications
Doner-specific anti-HLA Abs is contraindication for transplantation and the donor is considered as non-compatible
Cross matching all potential donors and recipients before transplantation can avoid DSA
Limited access to transplantation of the sensitized candidate can be controlled by how broadly their Anti-HLA Abs react with the potential donor population
PRA is the measure of sensitization to predict the probability to find a compatible donor for kidney transplantation
Is done by using a panel of normal blood-donors as representative of the potential local organ donor pool and patient’s serum,the percentage of this pool of donors to which a patient had reactive Abs is called PRA.
A patient with 80% PRA would be crossmatch incompatible with 80%of donors.
Because of lacking organized guidelines for labs to indicate which PRA should be used ,many Labs chose the highest PRA value among their test platforms
CPRA is based upon unacceptable HLA Ags to which the patients has been sensitized and which,if present in a donor, mean unacceptable risk for the candidate or transplant program.
CPRA represent the percentage of actual organ donors that express one or more of these unacceptable HLA Ags and it is computed from HLA Ags frequencies among 12,000 kidney donors.
The percentage of the people from general population carring that unacceptable Ag is the CPRA of that patient
CPRA provides a more accurate estimate of sensitization because it include both class l and class lol HLA specificities in the calculation which is a major shift from the traditional PRA where class l and class lol specificities are measured separately.
In traditional PRA, a high value mean a high probability of a positive crossmatch.
While in CPRA, a high value should mean a high probability of a negative crossmatch.
Because of the difference between transplant patient program and their laboratories in defining unacceptable Ags , communication between histocompatibility laboratories and the transplant program is critical element for the success of this new method for assessing sensitization levels.
CPRA is a tool for characterizing and monitoring sensitization.
CPRA provide estimate of transplantability for most patients.
PRA is a test used to assess the patient sensitization pre transplantation. It estimate the recipient antibodies against HLA antigens in candidate donors in the regional pool by mixing the recipient serum with the lymphocytes of the candidate donors and estimating the percentage of the positive reactions.
Calculated PRA is more accurate than PRA. It uses a newer technique to detect the unacceptable HLA antigens and the percentage of donors that the patient has antibodies against their unacceptable HLA antigens.
Sensitization means the presence of preformed antibodies or the potential to form antibodies against HLA antigens post transplant, hence acute rejection, delayed graft function, and the need for aggressive immunotherapy and the exposure to their side effects
Thanks, Dr Mahmoud
What is the difference in the size of the panel between PRA and cPRA?
What are the techniques used in both?
Calculated PRA use wider pool than PRA.
PRA is calculated by cross match based on cytotoxicity method, while calculated PRA is based on solid phase antibody testing.
FORM THE BEGINING OF ERA OF KIDNEY TRANSPLANTION, REJECTING THE KIDNEY WAS THE PROBLEM THAT SHOULD BE SOLVED BY PHYSICIANS .
ONCE HLA DISCOVERD ,IT WAS THE STARTING POINT AT WHICH NEW ERA HAD BEGUN,.
BUT THE PROBLEM WAS THAT MANY PT HAD ALOT OF ANTIBODIES AGANIST THEIR DONORS ,(DSA, DONOR SPECIFIC ANTIBODIES )WHICH PUT THE PT AT HIGH RISK OF REJECTIONS .
HERE PRA(PANEL RAECTIVE ANTIBODY) HAD SOLVED THIS ISSUE, AS ADDING RECPIENT SERUM AGAINST A POOL OF DONORS SERUM WILL ALLOW US TO KNOW HOW MUCH ANTIBIDIES THAT THE RECPIENT HAS AGAINST PERCENTAGE OF POULATION.
THE HIGHER THE PRA THE LESS CHANCE OF TRANSPLANTION.
ON 2007 UNOS IMPLENTED cPRA, WHICH DETERMINES THE FREQUENCY OF INCOMPATIBLE DONOR HLA PHENOTYPES BASED ON UNNACCPTEABLE CLASS 1,2 HLA ANTIGENS THAT HAVE BEEN LISTED FOR EACH CANDIDTAE , SINCE HLA-A, B,C -DR AND DQ SUBTYPES OF ACTUAL DECESD KIDNEY DONORS WERE USED TO COMPUTE ANTIGEN FREQUENCIES, THE c-PRA RFLECTS THE TRUE PROBALITY OF INCOMAPTIBLE DONOR BASED ON UNACCEPTATBLE ANTIGENS THAT HAVE BEEN LISTED FOR A PTIENT.
THOSE WHO HAVE HIGH PRA TENDS TO HAVE LESS CHANCES OF TRANSPLANTION,AS MENTIONED BEFOR
DESENTIZTION PRTOCOL INCLUUIDING PLASMAPHAREISIS AND IV IGG AND ANTI CD20 , WILL HELP TO DECREASE THEIR ANTIBIDIES TO SOME EXTENT,ABUT ITS SO COSTLY AND WAITING LIST ALSO ON DD LIST MAY BE TOO LONG FOR THE PT ,SO PAIRED EXCHANGE PROGRAMM SHOULD BE OFFERED IF HE HAS LIVING DONOR .
AND IF SOME CENTES DOSENT HAVE PAIRED EXCHANGE PROGRAMM, ACCEPTING HLA INCOMAPTIBLE EITHER FROM LIVING OR DECAESD TRANSPLANTION MAY BE RISKY (AMR RTAE VERY HIGH) BUT SOME STUDIES SHOWED IMPROVED GRAFT SURVIVAL COMAPRED WITH THE PT WHO REMAINED ON WAITING LIST.
Thanks Dear Mohammed
Please rewrite your reply in in a sentence style rather than in capital letters. Capital letter writing is not user friendly
Sure
PRA is a method to measure sensitivity of transplant patient , it represents percentage of donors to which the patient have reactive antibodies
It is measured through mixing recipient blood with panel of donor lymphocytes .
Patient with PRA 80% , means that the recipients reacts with 80% of the available donor
Calculated PRA depend on the percentage of inacceptable HLA antigens ,to which the patient is highly sensitized against ,
Prepared from antigens of actual donors ( 12000 actual donor )
It is measured using luminex technology , allowing for more specific detection of anti HLA antibodies and their actual strength allowing to discard less clinically important antibodies and define inacceptable antigens ,
This is to facilitate transplantation in broadly sensitized patients.
Application of CPRA reduced waiting lists of broadly sensitized patients
Calculated PRA is more accurate in detecting sensitization than PRA as it involves both class I and class II together
Sensitized patients can develop hyperacute rejection ,accelerated acute rejection , antibody mediated rejection , delayed graft functions and many other adverse events on the long run .
PANEL REACTIVE Antibody is a test to detect sensitization among transplantation candidate, the higher the test the more possibility for rejection unless more effective and potent strategies were deployed.
One difference between PRA and cPRA is the number of donors being 100 in the first and 12000 in the second. another difference is that cPRA is more uniform than PRA.
sensitized patients are more prone for graft rejection. as the have more antibodies against donor HLA system in the graft.
What is the PRA and how it is calculated?
PRA has been the measure of sensitization; it is a test that could identify sensitized patients and estimate their likelihood of finding a crossmatch-compatible donor using a panel of normal blood donors as representative of the potential local organ donor pool. PRA was simply the percentage of this pool of donors to which a patient had reactive antibodies. A patient with 80% PRA would be crossmatched incompatible with 80% of donors
What is the difference between PRA cPRA (cRF)?
Like PRA, CPRA is a tool for characterizing and monitoring sensitization. Unlike PRA, the CPRA provides a meaningful estimate of transplant ability for most patients, because it is calculated from unacceptable HLA antigens that will preclude offers from predictably crossmatch incompatible donors.
CPRA provides a more accurate estimate of sensitization because it includes both class I and class II HLA specificities in the calculation, a major departure from traditional PRA, where class I and class II specificities are measured separately. Even B-cell panels, which express both class I, and class II antigens are generally constructed to cover the class II HLA antigens and are not representative of HLA distributions in the general population.
Sensitization remains a formidable barrier to transplantation. Patients who have performed antibodies against HLA antigens are at risk for hyperacute rejection, accelerated acute rejection, antibody-mediated rejection, delayed graft function and longer-term complications when
transplanted from a donor expressing the target HLA antigens. We avoid donor-specific antibodies by crossmatching all potential donors and recipients before transplantation, and as a result, sensitized transplant candidates have limited access to transplantation in proportion to how broadly their anti-HLA antibodies react with the potential donor population.
1-Panel reactive antibody (PRA)
is a screening test to identify the presence of antibodies to HLA antigens by adding the patient’s serum to a panel of cells from multiple donors (ideally drawn from the region where the recipient resides).
The percentage of panel cells that are lysed by the serum is then calculated. A 50 % score means that half of the (regional) donor pool or population is expected to give a positive cross match.
A score of more than 20 % indicates that the recipient is sensitized.
The calculated CPRA
is based upon unacceptable HLA antigens to which the patient has been sensitized and which, if present in a donor, would represent an unacceptable risk for the candidate or the transplant program.
The terms “calculated HLA antibody reaction frequency” (cRF) and “calculated panel reactive antibod- ies” (cPRA) are used synonymously to describe the level of allosensitization, where 0% cRF is nonsensitized, 50% cRF is antibody incompatible with half of a random donor pool, and 90% cRF would be antibody incompatible with 9 out of 10 random donors.
HLA mismatches from a previous transplant and mismatched after pregnancy may considered unacceptable.
2- In the lower PRA groups, CPRA tended to be higher, whereas some patients in the 80+%PRA group did not have sufficient unacceptable antigens reported to warrant this CPRA level
CPRA provides a more accurate estimate of sensitization because it includes both class I and class II HLA specificities in the calculation, a major departure from traditional PRA, where class I and class II specificities are measured separately.
traditional PRA value meant a high probability of a positive crossmatch
high CPRA value should mean a high probability of a negative crossmatch
3- Patients who have preformed antibodies against HLA antigens are at risk for hyperacute rejection, accelerated acute rejection, antibody-mediated rejection, delayed graft function and longer term complications when transplanted from a donor expressing the target HLA antigens.
Thanks, Dalia
I really like your answer and the language used.
Dear All
What about the consistency of the PRA results?
Can the PRA differ between labs?
PRA results depend on the most the kit used for the test (the panel of HLA antigen) as well the technique used (CDC/ Solid phase immunoassays). Hence the results may be inconsistent. For example, the test panel might not be representative of the donor pool of the community. Similarly, the sensitivity levels of the techniques to detect PRA vary.
For the same reason , the results can vary in 2 different labs, if they use different methods or different test kits
Yes may be, due to False positive reactions against HLA class II Molecules detected in Luminex single antigen bead assays ??
yes the PRA reporting are quite variables that’s why the UNOS implemented anew policy since 2007 by addressing the use of new different cell panels test called the calculated PRA which refer to testing the frequency of incompatible donor HLA phenotypes based on unacceptable class 1and class11 HLA antigens so the CPRA reflects the true probability of incompatible donor based on the unacceptable antigens that have been listed for a patient
for example A CPRA OF 80% means 80% of DD Kidneys are not acceptable
traditional PRA value meant a high probability of a positive crossmatch
high CPRA value should mean a high probability of a negative crossmatch
are these opposite to each other, please
for example, A CPRA OF 80% means 80% of DD Kidneys are not acceptable
PRA(panel reactive antibody ) is a complement-fixating assay to detect the ability of recipient’s ability to cause lysis of potential donors T cells.
PRA detects only anti-HLA I antibodies so doesnot represent all the donors . If positive T-cell cross-match is there ,it will be an absolute contraindication to kidney transplantation due to high-risk for hyper-acute rejection. A positive B-cell cross-match is associated with a high-risk of hyperacute rejection.(1)
The calculated panel-reactive antibody (CPRA) value is the percentage of donors supposed to have unacceptable antigens presented on the waiting list . Unacceptable antigens are lab detection of HLA-specific antibodies by a solid-phase immunoassay . The transplantation center added criteria for unacceptable antigens, such as repeat transplant mismatches. The CPRA value is automatically calculated as soon as the unacceptable antigens are updated on the waiting list. The CPRA is derived from HLA antigen and haplotype frequencies for the different ethnic groups in proportion to their representations in the national deceased-donors.(2)
Both PRA and CPRA identify and monitor sensitisation, but CPRA provides a more precise estimate of sensitization because it includes both class I and class II HLA specificities in the calculation, making it better than PRA, as class I and class II are detected separately
-panel reactive antibody testing is important in order to identify the possible presence of anti HLA antibodies and lower the possibility of occurrence of antibody medicated rejection.
Ahigh PRA value indicates a positive cross match but an offer to patient with high CPAR indicates higher possibility of negative cross match preventing offers from donors patient is highly sensitised to because patients with antibodies against HLA antigens are susceptible to hyperacute ,accelerated acute ,or antibody mediated rejection ,as well as long term complications
1-Ashton Chen, … Andrew M. South, in Kidney Transplantation, Bioengineering and Regeneration, 2017
2-Bertram L. Kasiske, Jeffrey J. Connaire, in Primer on Kidney Diseases (Fifth Edition), 2009
Thanks, nice collection
please, could explain this to me more
Ahigh PRA value indicates a positive cross match but an offer to patient with high CPAR indicates higher possibility of negative cross match preventing offers from donors patient is highly sensitised to because patients with antibodies against HLA antigens are susceptible to hyperacute ,accelerated acute ,or antibody mediated rejection ,as well as long term complications