The Impact of BMI on Perioperative Urine Volume and Renal Function in Living Donor Kidney Transplantation

Introduction: Obesity is a well-recognized risk factor for various systemic disorders and has also been shown to influence perioperative outcomes in surgical fields. In the context of living donor kidney transplantation (LDKT), increased BMI has been associated with greater technical complexity and a higher incidence of postoperative complications, including wound infection and delayed graft function (DGF). We explored the impact of BMI on the perioperative urine volume (UV) and renal function in LDKT. Methods: We conducted a retrospective analysis at a single institution to assess the impact of BMI on outcomes following LDKT. Patients were stratified according to BMI into the obese group (Og) (BMI ≥ 25 kg/m²) and the non-obese group (nOg) (BMI < 25 kg/m²). Between April 2010 and December 2024, 118 patients underwent LDKT at Oita University Hospital. After excluding patients who experienced acute rejection, underwent repeat kidney transplantation, or developed vesicoureteral anastomotic complications, 109 patients remained eligible for analysis. We compared outcomes and UV within 14 days postoperatively, and renal function between the Og and nOg. The mean (SD) postoperative follow-up period was 79.7(47.2) months in the nOg and 56.1 months (47.5) in the Og (p = 0.0156). Results: A total of 109 patients were analyzed, comprising 36 patients in the Og and 73 in the nOg. Baseline demographic and clinical characteristics were generally comparable between the two groups, including age, sex, comorbidity, donor BMI, duration from dialysis initiation to transplantation, immunosuppressive regimens. However, baseline serum creatinine levels were significantly higher in obese recipients than in non-obese recipients (p = 0.005). Postoperatively, UV on postoperative day 1 (POD 1) was significantly lower in the Og (p = 0.02). Furthermore, the mean rate of creatinine reduction and the mean estimated glomerular filtration rate (eGFR) increase were significantly higher in the nOg from POD1 to POD4 (p<0.05). No significant differences were observed with respect to warm ischemia time (WIT), total ischemia time (TIT), length of hospital stay, or the incidence of postoperative complications. Multivariate analysis identified obesity as an independent predictor of reduced UV on POD1 (p = 0.00978). Conclusion: Obese recipients undergoing LDKT demonstrated significantly lower UV on POD1 and a slower initial recovery of graft function. However, these early physiological differences did not translate into a higher incidence of major postoperative complications or prolonged length of hospital stay. These findings suggest that although early UV may be lower in obese recipients, careful and individualized perioperative fluid management is essential to maintain adequate graft perfusion.