Impact of the 2014 kidney allocation system changes on trends in A2/A2B into B kidney transplantation and organ procurement organization reporting of donor subtyping

A2/A2B Deceased Donor Kidney Transplantation Using A2 Titers Improves Access to Kidney Transplantation: A Single-Center Study

Rationale & Objective

The option for A2/A2B deceased donor kidney transplantation was integrated into the kidney allocation system in 2014 to improve access for B blood group waitlist candidates. Despite excellent reported outcomes, center uptake has remained low across the United States. Here, we examined the effect of implementing an A2/A2B protocol using a cutoff titer of ≤1:8 for IgG and ≤1:16 for IgM on blood group B kidney transplant recipients at a single center.

Study Design

Retrospective observational study.

Setting & Participants

Blood group B recipients of deceased donor kidney transplants at a single center from January 1, 2019, to December 2022.

Exposure

Recipients of deceased donor kidney transplants were analyzed based on donor blood type with comparisons of A2/A2B versus blood group compatible.

Outcomes

One-year patient survival, death-censored allograft function, primary nonfunction, delayed graft function, allograft function as measured using serum creatinine levels and estimated glomerular filtration rate at 1 year, biopsy-proven rejection, and need for plasmapheresis.

Analytical Approach

Comparison between the A2/A2B and compatible groups were performed using the Fisher test or the χ2 test for categorical variables and the nonparametric Wilcoxon rank-sum test for continuous variables.

Results

A total of 104 blood type B patients received a deceased donor kidney transplant at our center during the study period, 49 (47.1%) of whom received an A2/A2B transplant. Waiting time was lower in A2/A2B recipients compared with blood group compatible recipients (57.9 months vs 74.7 months, P = 0.01). A2/A2B recipients were more likely to receive a donor after cardiac death (24.5% vs 1.8%, P < 0.05) and experience delayed graft function (65.3% vs 41.8%). There were no observed differences in the average serum creatinine level or estimated glomerular filtration rate at 1 month, 3 months, and 1 year post kidney transplantation, acute rejection, or primary nonfunction.

Limitations

Single-center study. Small cohort size limiting outcome analysis.

Conclusions

Implementation of an A2/A2B protocol increased transplant volumes of blood group B waitlisted patients by 83.6% and decreased the waiting time for transplantation by 22.5% with similar transplant outcomes.

A2/A2B to B deceased donor kidney transplantation in the Kidney Allocation System era

Kidney transplantation from blood type A2/A2B donors to type B recipients (A2→B) has increased dramatically under the current Kidney Allocation System (KAS). Among living donor transplant recipients, A2-incompatible transplants are associated with an increased risk of all-cause and death-censored graft failure. In light of this, we used data from the Scientific Registry of Transplant Recipients from December 2014 until June 2022 to evaluate the association between A2→B listing and time to deceased donor kidney transplantation (DDKT) and post-DDKT outcomes for A2→B recipients. Among 53 409 type B waitlist registrants, only 12.6% were listed as eligible to accept A2→B offers ("A2-eligible"). The rates of DDKT at 1-, 3-, and 5-years were 32.1%, 61.4%, and 72.1% among A2-eligible candidates and 14.1%, 29.9%, and 44.1% among A2-ineligible candidates, with the former experiencing a 133% higher rate of DDKT (Cox weighted hazard ratio (wHR) = 2.192.332.47; P < .001). The 7-year adjusted mortality was comparable between A2→B and B-ABOc (type B/O donors to B recipients) recipients (wHR 0.780.941.13, P = .5). Moreover, there was no difference between A2→B vs B-ABOc DDKT recipients with regards to death-censored graft failure (wHR 0.771.001.29, P > .9) or all-cause graft loss (wHR 0.820.961.12, P = .6). Following its broader adoption since the implementation of the kidney allocation system, A2→B DDKT appears to be a safe and effective transplant modality for eligible candidates. As such, A2→B listing for eligible type B candidates should be expanded.

Increasing Access to Kidney Transplantation for Black and Asian Patients Through Modification of the Current A2 to B Allocation Policy

Key Points

A2 to B incompatible transplantation is not fully practiced in the country, and further policies should encourage centers to perform more blood incompatible transplants. Centers that currently practice A2 to B incompatible transplants should give priority to blood type B patients who are willing to accept an A organ. This will benefit Asian and Black patients.

Background

The rate of A2 to B incompatible (ABO-i) kidney transplant continues to be low despite measures in the new kidney allocation system (KAS) to facilitate such transplants. This study shows how the number of ABO-i transplants could increase if KAS policies were used to their fullest extent through a boost in ABO-i priority points.

Method

Transplant outcomes were predicted using the Kidney Pancreas Simulated Allocation Model, preloaded with national data of 2010. We used this simulation to compare KAS with a new intervention in which priority equal to cPRA=100 has been given to blood type B candidates who are willing to accept an A blood type organ.

Results

The number of Black recipients increased by 375 (from 35% of the total recipient population to 38.7%), the number of blood type B Blacks increased by 65 (from 8% of the total recipient population to 9%), and the number of blood type B Black patients receiving blood type A kidneys increased by 49 (from 2% of the total recipient population to 2.5%). The same change occurred for Asians, particularly blood type B Asians (from 0.54% of the total recipient population to 0.7%). The average wait time notably decreased by 27 days for blood type B Black patients. In the proposed scenario, 263 blood type B Black patients received a blood type A organ (2.5% of the total recipient population) while only 181 (1.1%) of such transplants were performed in 2021. These results signify a considerable opportunity loss of ABO-i transplants for Black patients.

Conclusions

If this policy was universally adopted, we would expect to see an overall increase in A2 to B transplantation, but in reality, not all centers perform ABO-i transplantation. Thus, adopting this policy would incentivize other centers to perform more subtyping of A-type kidneys, and it would increase access to organs for blood type B Asian and Black patients in centers where ABO-i transplantation already takes place.