Introduction: Discrepancies between donor and recipient body size can lead to glomerular hyperfiltration or underfiltration, potentially compromising long-term graft survival and function. This study investigates the impact of kidney size mismatch, assessed by the body surface area (BSA) ratio, on death-censored graft failure and estimated glomerular filtration rates (eGFR) in deceased donor kidney transplant (DDKT) recipients.
Method: We retrospectively analyzed adult DDKT recipients from Ramathibodi Hospital between January 2010 and December 2022. Recipients were categorized into three groups based on the body surface area donor-to-recipient (BSA D:R) ratio. Cut-offs were defined using ±1 standard deviation (SD) from the mean BSA D:R of the entire cohort, creating small-donor (BSA D:R < 0.90), match-donor (BSA D:R 0.90–1.25), and large-donor (BSA D:R > 1.25) groups. Kaplan-Meier analysis and the log-rank test was used to evaluate death-censored graft failure among the groups. Cox-proportional hazard models were used to identify factors affecting graft failure. We used mixed-effects linear regression to analyze the eGFR trajectories within and across each category over the follow-up period.
Results: of 1,094 DDKT recipients, 185 (17%) were classified as small donors, 743 (67%) as matched donors, and 166 (16%) as large donors. Baseline graft quality was comparable across groups. Over a median (IQR) follow-up of 4.7 (5.1) years, 121 patients experienced death-censored graft failure. Kaplan-Meier analysis with log-rank test (p = 0.007) demonstrated a significant difference in graft failure among recipient groups based on BSA D:R ratio.
 
After adjusting for donor and recipient age, expanded criteria donor status, acute kidney injury in the donor, and HLA mismatch, recipients in the small-donor group had a 2.03-fold increased risk of graft failure compared to the match-donor groups (adjusted HR: 2.03, 95% CI: 1.32–3.14, p <0.01). No significant diferrence in graft failure risk was observed between the large-donor and match-donor groups (adjusted HR: 0.81, 95%CI: 0.40–1.39, p = 0.45). Within each group, after adjusting for baseline eGFR at 30 days post-transplant, the match-donor and small-donor groups exhibited similar eGFR trajectories over time. In contrast, the large-donor group displayed a significantly slower decline in eGFR compared to the small-donor group (mean difference: 2.2 ml/min/1.73 m², p = 0.04) (Figure 2).
Conclusions: This study demonstrates that recipients with small donor kidneys experience a significantly increased risk of death-censored graft failure compared to those receiving match-sized or large donor kidneys. This finding highlights the importance of considering kidney size mismatch as a factor influencing long-term graft function following DDKT.