Allocating Deceased Donor Kidneys to Candidates with High Panel-Reactive Antibodies

Abstract

Background and objectives: In December of 2014, the Organ Procurement and Transplant Network implemented a new Kidney Allocation System (KAS) for deceased donor transplant, with increased priority for highly sensitized candidates (calculated panel-reactive antibody [cPRA] >99%). We used a modified version of the new KAS to address issues of access and equity for these candidates.

Design, setting, participants, & measurements: In a simulation, 10,988 deceased donor kidneys transplanted into waitlisted recipients in 2010 were instead allocated to candidates with cPRA≥80% (n=18,004). Each candidate's unacceptable donor HLA antigens had been entered into the allocation system by the transplant center. In simulated match runs, kidneys were allocated sequentially to adult ABO identical or permissible candidates with cPRA 100%, 99%, 98%, etc. to 80%. Allocations were restricted to donor/recipient pairs with negative virtual crossmatches.

Results: The simulation indicated that 2111 of 10,988 kidneys (19.2%) would have been allocated to patients with cPRA 100% versus 74 of 10,988 (0.7%) that were actually transplanted. Of cPRA 100% candidates, 74% were predicted to be compatible with an average of six deceased donors; the remaining 26% seemed to be incompatible with every deceased donor organ that entered the system. Of kidneys actually allocated to cPRA 100% candidates in 2010, 66% (49 of 74) were six-antigen HLA matched/zero-antigen mismatched (HLA-A, -B, and -DR) with their recipients versus only 11% (237 of 2111) in the simulation. The simulation predicted that 10,356 of 14,433 (72%) candidates with cPRA 90%-100% could be allocated an organ compared with 7.3% who actually underwent transplant.

Conclusions: Data in this simulation are consistent with early results of the new KAS; specifically, nearly 20% of deceased donor kidneys were (virtually) compatible with cPRA 100% candidates. Although most of these candidates were predicted to be compatible with multiple donors, approximately one-quarter are unlikely to receive a single offer.

Keywords: HLA antigens; adult; humans; kidney; kidney transplantation; tissue donors; transplant outcomes; transplantation.

Figure 1.

Graphic representation of 2010 adult kidney–alone waitlisted candidates according to race and calculated panel–reactive antibody (cPRA) percentages. The distribution of candidate race within cPRA category is shown on the x axis, and the percentage of candidates by race within cPRA group is shown on the y axis; the total in each cPRA group equals 100%.

Figure 2.

Median compatible donors by broad calculated panel–reactive antibody (cPRA) category among adult kidney‐alone waitlisted candidates in 2010. Each donor (n=6141) was assessed for compatibility with each candidate (n=18,004) with cPRA ≥80%. The median number of donors compatible with candidates at specific cPRA levels is displayed at the top of each bar.

Figure 3.

Racial distribution of candidates with calculated panel–reactive antibody 100% (n=1398) who were incompatible with every deceased donor kidney transplanted in 2010. Higher percentages of black, Hispanic, Asian, and Native American candidates than of white candidates were incompatible with all donors.

Figure 4.

Percentage of six antigen–matched/zero antigen–mismatched kidneys allocated to patients by incremental calculated panel–reactive antibody (cPRA) levels that were actually transplanted in 2010 and as simulated, respectively. Total six antigen HLA–matched/zero antigen–mismatched transplants: actual, 269; simulated, 308.