Clinical outcomes and prognostic factors of ABO-incompatible kidney transplantation: A single-center retrospective study using propensity score matching 

Background: To mitigate the chronic shortage of donor organs, the ABO-incompatible (ABOi) kidney transplantation (KT) has emerged as a crucial therapeutic strategy for end stage kidney disease (ESKD) patients. Refinements in pre-transplant desensitization along with advanced immunosuppressive management have rendered ABOi KT a safe and viable option. This study aims to evaluate the long-term clinical outcomes and identify prognostic factors of ABOi KT within single-institution cohort. 
Methods: This retrospective study analyzed 137 ABOi KT recipients (2013–2024) and 388 ABO-compatible (ABOc) KT recipients (2005–2024) at Seoul National University Bundang Hospital (SNUBH). To ensure comparability, 1:2 propensity score matching (PSM) was performed based on the factors such as age, sex, causes of chronic kidney disease (CKD), the number of Human leukocyte antigen (HLA) mismatches and panel reactive antibody (PRA) levels. A balanced cohort of 355 patients (ABOi, n=136; ABOc, n=219) was established, with all covariates achieving a standardized mean difference (SMD) < 0.1. 

Results: In the comparison of overall clinical outcomes, no statistically significant differences were observed in graft failure (p=0.498), mortality (p=0.586), and delayed graft function (DGF) (p=0.995). Although the incidence of rejection—comprising both biopsy-proven cases and clinically suspected episodes managed without biopsy—was significantly higher in the ABOi group (36.8% vs. 26.0%, p=0.032; OR=1.652), it did not imply inferior graft or patient survival. Kaplan-Meier analysis showed no significant difference between the two cohorts; the 3-year and 5-year death censored graft survival (DCGS) rates were 94.3% and 94.3% in the ABOi group, and 99.0% and 98.2% in the ABOc group, respectively (p = 0.22). The 3-year and 5-year patient survival rates were 99.2% and 99.2% for the ABOi group, and 97.7% and 96.9% for the ABOc group (p = 0.64). Univariate analysis within the ABOi group identified postoperative surgical complications (HR 5.692, p=0.037) and infectious complications (specifically CMV infection, HR 8.841, p=0.009) as significant risk factors for graft loss. Conversely, kidney weight (HR 0.966, p=0.030) was a protective factor. Regarding patient survival, longer pre-transplant dialysis duration (HR 1.027, p=0.041) was the only significant risk factor.
Conclusion: ABOi KT demonstrates equivalent long-term graft and patient survival comparable to ABOc KT, despite higher immunological risks. Our findings suggest that the success of ABOi KT is predominantly influenced by perioperative complication management rather than baseline characteristics. Therefore, meticulous monitoring for adverse events of surgical issues and infections especially, CMV is paramount for optimizing outcomes. ABOi KT remains a safe and reliable option to expand the donor pool and improve access to transplantation.