Effect of HLA Matching on the Relative Risk of Mortality for Kidney Recipients: a Comparison of the Mortality Risk After Transplant to the Mortality Risk of Remaining on the Waiting List

Background: Patients must wait increasingly longer periods on the kidney waiting list (WL) before receiving a transplant. Although patients can be maintained on dialysis, many deaths occur while waiting. To determine whether the risk of mortality on the WL is different from that related to the transplant procedure, data from the Organ Procurement and Transplantation Network and Scientific Registry were used to analyze all adult patients entered on the United Network for Organ Sharing (UNOS) kidney WL for a primary transplant between April 1, 1994, and December 31, 1994 (n=9925).

Methods: To account for the time spent on the WL before transplant, a time dependent, nonproportional hazards model was used to assess the risk of mortality after transplant for both well-matched (zero to two HLA mismatches) and poorly-matched (three to six HLA mismatches) transplants compared with the mortality risk of remaining on the WL. This model incorporated an exponential decay component to account for the transient increased risk after kidney transplantation. Patients were stratified by age, race, creatinine level, panel-reactive antibody at listing, and blood group.

Results: Although there was an increased risk of mortality in the initial posttransplant period, the risk of mortality at 1 year for transplanted patients was 59% (three to six mismatches) to 67% (zero to two mismatches) less than that of patients who remained on the waiting list for an additional year.

Conclusions: Kidney transplantation is more beneficial than remaining on the waiting list. Even poorly-matched kidneys provided a significant reduction in the risk of mortality by 6 months as compared with the mortality risk of continuing to wait. Patients receive the maximum benefit when transplanted with well-matched kidneys.