*Purpose: Delayed kidney transplantation for patients undergoing combined liver-kidney transplant (CLKT) have been suggested to improve patient survival and kidney function compared to simultaneous liver-kidney transplantation (SLK). This study aims to validate the efficacy of delayed SLK using the United Network Organ Sharing (UNOS) registry.

*Methods: We examined all adult CLKT transplanted from Jan 01 2003 to Mar 31 2017 in the UNOS registry. Delayed CLKT was defined as the difference between kidney and liver cold ischemia time (CIT Difference) ≥24 hours whereas SLK was defined as CIT Difference ≤6 hours. Multivariable cox proportional hazards and propensity score matching models were fitted to compare patient and graft outcomes between those who underwent delayed CLKT versus SLK.

*Results: 5816 adult CLKT were included in this study with 4460 SLK and 915 delayed CLKT. The mean CIT difference was 6.07 (± 3.13) hours. Delayed CLKT was associated with worse 1-year patient (HR = 1.42, P = 0.036), liver (HR = 1.44, P = 0.024), and kidney (HR = 1.45, P = 0.021) survival compared to traditional SLK in those with high MELD scores (MELD ≥35). Amongst those with low (MELD ≤25) or medium (MELD 26-34) MELD scores, delayed CLKT had no significant impact on patient or graft outcomes. Delayed CLKT was a protective factor against the development of delayed kidney graft function (DGF) across all MELD score categories (OR = 0.71, P<0.001). No significant differences in 3, 6, or 12-month eGFR were observed between delayed CLKT and SLK.

*Conclusions: Delayed CLKT is associated with worse 1-year patient, liver, and kidney survival in those with MELD ≥35, is protective against the development of DGF across all MELD score categorizations and have comparable post-transplant kidney function compared to SLK. Risk stratification based on MELD scoring should be considered among patients receiving delayed CLKT.

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