*Purpose: Living donor kidney transplantation (LDKT) continues to become a more prevalent treatment method for ESRD and is known to increase both organ availability and graft survival. While it has been shown that matching donor and recipient characteristics (age, sex, biological relation, HLA) can improve long-term outcomes, the extent to which these factors affect graft longevity has not been extensively described. Determining the influence that each of these characteristics have on graft lifetime may aid in creating criteria for optimizing donor selection, especially for patient-donor pairs participating in kidney paired donation (KPD). This study identifies the effect of individual donor and recipient characteristics on graft survival in LDKT using a recently described novel measure, kidney life years (KLYs)

*Methods: The OPTN/UNOS database was used to identify patients who were first-time kidney-only LDKT recipients between 1987 and 2020 (n=147,316). This population was divided into those who experienced death with a functioning graft (DWFG) (n=20,575) and those who did not (n=126,741). In the population without DWFG, after excluding cases with missing information, 88,940 cases were analyzed. IBM SPSS software version 28.0.0 was used to apply Cox and multiple regression analyses to the dataset, with the dependent variable being KLYs.

*Results: Of the 18 donor and recipient variables investigated, all but Donor Sex Male – Recipient Sex Female (HR=_0.9991.041_1.086; P=0.054) were determined to be statistically significant (P<0.05) on univariable Cox regression analysis. On multivariable Cox regression analysis, after adjusting for recipient characteristics, Donor Age (HR per 10y=_1.1101.120_1.140 P<0.001), Donor Sex Male - Recipient Sex Male (HR=_0.8000.843_0.887; P<0.001), Donor BMI (HR per unit=_1.0051.008_1.012; P<0.001), ABO Incompatible (HR=_1.2031.382_1.586; P<0.001), HLA Match (HR per 50pts=_0.7000.700_0.750; P<0.001), and Donor African American Race (HR=_1.6041.673_1.745; P<0.001) were found to be the most significant factors determining graft failure. Donor Age (_-0.036-0.030_-0.025 KLYs; P<0.001), Donor BMI (_-0.074-0.060_-0.045 KLYs; P<0.001), HLA Match (_0.0190.022_0.024 KLYs; P<0.001), and Donor African American Race (_-2.577-2.383_-2.188 KLYs; P<0.001) had the largest influence on the dependent variable, KLYs, based on multiple linear regression.

*Conclusions: Several donor and recipient factors are associated with significant effects on kidney graft longevity. Notably, increasing donor-recipient HLA match points by 50 was shown to add an additional 1.1 KLYs, whereas increasing donor age by 10 years resulted in only a -0.3 KLY decrease. Determining graft longevity in KLYs based on patient and donor characteristics may have an application in optimizing LDKT donor selection.

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