The new OPTN Kidney Allocation System: An early look at the transplant trend in the highly sensitized patient cohort

Abstract

Aim The new OPTN Kidney Allocation System (KAS) is expected to prioritize highly sensitized candidates nationwide. Many of these candidates are likely to have antibodies to DP and/or DQA antigens, which are not accounted for in the assessment of cPRA and unacceptable antigens listed in UNOS. This can compromise the feasibility of performing reliable virtual crossmatches (XMs). Herein, we evaluated the impact of new KAS thus far, on kidney allocation for highly sensitized candidates of cPRA ⩾ 98%. Methods Data was collected from the 8 renal transplant centers in Michigan for recipients with cPRA ⩾ 98%, between Dec 4, 2014 and Apr 6, 2015 and the same 4-month period of the previous four years. In this cohort, we evaluated: (1) number of kidney offers; (2) frequency of DP/DQA antibodies; (3) “unexpected” positive XMs; (4) transplant rates; (5) number of out-of-state kidney offers; and (6) kidney discard rate. Results The number of kidney offers to recipients with cPRA ⩾ 98% revealed a 160% increase, from 5 pre-KAS to 13 post-KAS offers/month. Antibodies to DP and/or DQA were present in 58% of these recipients (30/52), and “unexpected” B-cell positive XMs due to such antibodies were observed in 30% of the XMs (9/30). Overall, the transplant rate for this group increased significantly to 42% (22 transplanted/52 offers) in comparison to a total of 13% (11/82) from the same time period in the past 4 years. Approximately, 1/3 of transplanted recipients from the new-KAS cohort had DP/DQA antibodies. In addition, since the new KAS, out-of-state kidney offers increased significantly by 11-fold to 33 in the 4-month period compared to that of the previous 4 years. Lastly, kidney discard rate slightly elevated to 22% (10 discards/46 kidneys) compared to an average of 17% (4/23), which could in part be attributed to the “unexpected” positive XMs. Conclusions To date, our data suggested that despite the unaccounted DP/DQA antibodies and “unexpected” positive XMs, the new KAS has enhanced organ allocation for the highly sensitized candidates, signified by the increased transplant rate. At this pace, we project 66 of these recipients in Michigan will be transplanted by year’s end. The increase in kidney discard rate especially due to positive XMs warrants further attention.