Horseshoe Kidneys in Transplantation: Underutilization Despite Comparable Quality and Favorable Outcomes: UNOS Registry Analysis (2007-2023)

Introduction: Horseshoe kidneys (HSKs) are the most common renal fusion anomaly, occurring in approximately 1 in 500 individuals and often discovered incidentally. Historically excluded from transplantation due to complex anatomy, advances in surgical techniques have made HSK transplantation increasingly feasible. Although successful procurement and transplantation have been described in case reports, national-level data comparing donor characteristics and organ utilization between HSK and non-HSK donors remain limited. This study characterizes donor demographics, clinical profiles, and organ utilization of HSK donors using the United Network for Organ Sharing (UNOS) database. Methods: A retrospective analysis of the UNOS kidney transplant registry was performed, including all deceased kidney donors from January 1, 2007, to September 30, 2023. Donors were stratified by the presence of a horseshoe kidney. HSK donors were matched 1:4 with non-HSK donors. Donor demographics, clinical characteristics, and organ disposition were compared using chi-square and t-tests. Results: A total of 235 HSK donors were identified. HSK donors were more often male (75.7% vs. 58.8%, p < 0.001) but otherwise similar in age, race, comorbidities, and kidney quality metrics including creatinine, KDPI, and KDRI (p > 0.05). Intravenous drug use was less common among HSK donors (5.6% vs. 11.3%, p=0.010). HSK donors more frequently died from blunt trauma and less often from intracranial hemorrhage (p=0.008). Despite comparable organ quality, transplanted kidneys from HSK donors were utilized less frequently (left: 59.2% vs. 79.5%; right: 48.6% vs. 78.0%, p < 0.001) and had longer cold ischemia times (22.3 vs. 17.9 hours, p < 0.001). Conclusions: HSK donors demonstrate comparable quality metrics to standard donors but are transplanted less frequently and experience longer cold ischemia times, suggesting underutilization of viable organs. Improved documentation of anatomical complexity and greater surgical familiarity may enhance acceptance and utilization.