Comparison of Kidney Allograft Outcomes in Simultaneous Liver-Kidney Versus Kidney After Liver Transplantation Since the Safety Net Era.

BACKGROUND

Criteria for simultaneous liver kidney transplantation (SLKT) have undergone several iterations. In August 2017, the Organ Procurement Transplantation Network (OPTN) created specific criteria for SLKT allocation and established a "safety net" protocol to allocate kidney allografts for liver transplant recipients with persistent renal dysfunction within the first year after liver transplantation (KALT). Published studies that evaluated patient and kidney allograft survival have applied the "safety net" criteria retrospectively to time periods prior to enactment of the policy. We aimed to assess kidney allograft outcomes in those who underwent KALT compared to those who underwent SLKT during the actual "safety net" era.

METHODS

This retrospective cohort study included adults (≥18 years) receiving a primary kidney transplant via SLKT or safety net KALT from 2018 to 2021, captured in the OPTN database. Patients receiving multiple organs other than kidney-liver, a kidney from a living donor, a split liver, or sequential or en bloc kidney transplant were excluded. Study outcomes, including kidney allograft survival, patient survival, eGFR and kidney rejection, were compared by KALT versus SLKT post-kidney transplant. Differences in eGFR and rejection for KALT versus SLKT were then assessed in a propensity score analysis (nearest neighbor matching [n = 4]) to estimate the conditional average treatment effect.

RESULTS

Between January 2018 and December 2021, 2620 patients underwent SLKT, and 526 underwent KALT by the safety net policy. Those who underwent KALT had a lower prevalence of diabetes mellitus (36.3% vs. 43.2%, p = 0.003). Alcohol as a reason for liver transplantation was higher in KALT versus SLKT (43.0 vs. 30.8%, p < 0.001). Recipients of KALT compared to SLKT had a higher prevalence of dialysis prior to transplant (73.2% vs. 53.5%, p < 0.001) with a higher median number of months of dialysis time (9.0 vs. 4.9 months, p < 0.001). At 1-year post-kidney transplant, KALT versus SLKT observed similar kidney allograft survival rates (97.7% [95%CI 96.0-98.7] vs. 96.8% [95%CI 96.0-97.4], p = 0.43) but higher patient survival rates (96.7% [95%CI 94.8-98.0] vs. 93.9% [95%CI 92.9-94.8] at 1 year [p = 0.02]). Those with KALT consistently had lower eGFR at 6 months, 1 year, and 3 years after kidney transplantation. The mean difference at 1 year was -6.6 mL/min/1.73 m (95% CI: -8.5 to -4.7, p < 0.001) in the unadjusted and -4.7 mL/min/1.73 m (95% CI: -7.0 to -2.4, p < 0.001) in the propensity score matched analysis. At the longest follow-up of 3 years, the mean difference remained -6.3 mL/min/1.73 m (95%CI: -8.8 to -3.7, p < 0.001) in the unadjusted and -3.8 mL/min/1.73 m (95% CI: -6.5 to -1.1, p = 0.005) in the propensity score matched analysis. While those with KALT had higher observed rates of rejection than SLKT throughout the period of 6 months, 1 year, and 3 years, propensity score matched analyses (adjusting for age, cPRA, HLA mismatch) did not show significant differences in rejection at all time points.

CONCLUSION

While kidney allograft survival was similar, KALT recipients had significantly lower eGFR than their SLKT counterparts. Currently, there are inadequate data to determine if these findings can be attributed to differences in rejection rates, and longer-term follow-up of kidney allograft outcomes is needed.