*Purpose: Deceased donor kidney allocation policies differ between solitary organs and combined transplants. The estimated waiting time for a kidney as part of a simultaneous pancreas-kidney (SPK) transplant is much shorter than that of a solitary kidney (SK). We sought to determine if the kidney-related outcomes of SPK transplants were comparable to SK transplants to justify preferential allocation.

*Methods: We performed a retrospective mate analysis of deceased donor kidney transplants included in the UNOS/OPTN database between October 1987 and March 2018 in which the kidney pair from a single donor was allocated as a SK and as part of a SPK. Exclusions included age <18 or >60; prior or simultaneous non-KP transplant. Recipient characteristics, transplant year, and transplant center volume were considered. Kaplan-Meier analysis and multivariable mixed-effect Cox regressions were performed of kidney pairs that were allocated as SK or part of a SPK transplant.

*Results: Overall, 31,608 kidney transplants (15,804 SK and 15,804 SPK) were included in our analysis. Compared to the SPK cohort, the SK cohort demonstrated an older recipient age (43 vs 40; p<0.001), a history of a prior transplant (19% vs 4%; p<0.001), greater preservation time (19 vs 13 hrs; p<0.001), a greater proportion of recipients on hemodialysis (HD; 89% vs 78%; p<0.001) with a longer duration on HD (3.5 vs 1.6 years; p<0.001). Kaplan-Meier analysis demonstrated lower patient (p<0.001), death-censored (p<0.001), and overall kidney-specific survival (p<0.001) for the SK cohort (Figure 1). In multivariable analysis, SPK recipients had worse patient survival than SK (HR 1.24, p = 0.025) but not overall or death-censored kidney-specific survival. Detrimental characteristics for kidney-specific survival were a history of a prior transplant (1.23, p = 0.049), increasing preservation time (1.11 for each 10 hr, p = 0.043), and African-American race (1.31, p = 0.001); waitlist time appeared to be protective (0.94, p = 0.01).

*Conclusions: Kidney allograft survival among SK and SPK recipients appears comparable in a contemporary cohort of the UNOS/OPTN database. Differences in kidney-specific survival appear to be most dependent on recipient characteristics.

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