*Purpose: The purpose of this study was to evaluate the pernicious effects of inadequate functional nephron mass in size disparate donation after cardiac death (DCD) kidney transplantation between pediatric donors and adult recipients by characterizing the impact of donor-recipient (D-R) body surface area (BSA) mismatch on long-term graft and patient survival.

*Methods: Utilizing the Organ Procurement and Transplantation Network (UNOS) database, a retrospective analysis was performed for all adult (18 years or older) recipients of pediatric (17 years or younger) DCD kidneys in the US from 1/1/2004-3/10/2020. The primary outcomes included death-censored graft survival, all-cause graft survival, and patient survival. The cohorts were defined by D-R BSA ratios of 0.10-0.70, >0.70-0.91, and >0.91.

*Results: Solitary DCD pediatric allografts transplanted between D-R pairs with a BSA ratio of 0.10-0.70 carried an increased risk of all-cause graft failure (RR 1.36; CI 1.10-1.69) and patient death (RR 1.32; CI 1.01-1.73) when compared to pairings with a ratio of >0.91. There was no difference in death-censored graft survival between these cohorts. Additionally, there was no difference in graft or patient survival between the >0.70-0.91 and >0.91 cohorts. Kaplan-Meier survival analysis revealed improved 10-year patient survival in recipients of en-bloc allografts (P = 0.02) compared to recipients of single kidneys with D-R BSA ratios of 0.10-0.70. A similar survival advantage was demonstrated in recipients of solitary allografts with D-R BSA ratios >0.70 (P = 0.02).

*Conclusions: Donor-recipient size disparity is associated with inferior patient and all-cause graft survivals, which can be overcome by appropriate BSA matching or en-bloc transplantation. The deleterious effects of mismatched D-R BSA ratios are likely attributed to the well described systemic sequelae of insufficient renal functional capacity. Therefore, D-R BSA matching is prognostically significant when considering allocation strategies for DCD kidneys from pediatric donors. Specifically, a D-R BSA ratio of >0.70 represents the safe lower limit for solitary kidney transplantation, while a ratio of 0.10-0.70 serves as criteria for en-bloc allocation.

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