Early Acute Kidney Injury in Allogeneic Hematopoietic Cell Transplantation: Incidence, Severity, and Associated Factors in a 634‐Recipient Cohort

ABSTRACT Background Acute kidney injury (AKI) is a frequent and clinically relevant complication in allogeneic hematopoietic cell transplantation (HCT) recipients, particularly during the early post‐HCT period. Although AKI has been extensively reported in long‐term follow‐up studies, data focusing on the initial hospitalization phase remain limited, despite its potential impact on subsequent clinical outcomes. Objective To evaluate the incidence, severity, and clinical and transplant‐related determinants of AKI during the first 3 weeks after allogeneic HCT. Methods We conducted a retrospective cohort study including 634 consecutive recipients undergoing allogeneic HCT between 2002 and 2023. AKI was defined according to KDIGO criteria and assessed from day +1 to day +21. Cumulative incidence was estimated, and associations were evaluated using Cox proportional hazards models. Pre‐AKI exposure to calcineurin inhibitors was analyzed. Results By day 21, AKI occurred in 346 patients (55%), and 27% of cases reached KDIGO stages 2–3. Median time to AKI was 12 days, with earlier onset among stage 3 events (median 5 days). In multivariable analysis, AST > 40 U/L was independently associated with an increased risk of any‐stage AKI (HR 1.58, 95% CI 1.17–2.12; p = 0.003), whereas albumin > 3.5 g/dL was protective (HR 0.56, 95% CI 0.44–0.71; p 40 U/L (HR 1.93, 95% CI 1.08–3.44; p = 0.025) and year of transplantation, with higher risk observed in earlier categories (2002–2008: HR 3.68, 95% CI 1.75–7.72; p < 0.001), while higher albumin levels remained inversely associated (HR 0.42, 95% CI 0.26–0.70; p < 0.001). Higher pre‐AKI cyclosporine trough levels (HR 1.11, 95% CI 1.05–1.17; p < 0.001) and a greater proportion of supratherapeutic days (HR 1.06, 95% CI 1.02–1.10; p = 0.005) were also associated with AKI. Conclusion Early AKI in HCT recipients is strongly associated with baseline clinical vulnerability, hepatic dysfunction, and calcineurin inhibitor exposure. Elevated AST and lower albumin levels identify patients at increased risk, while higher cyclosporine exposure contributes to early renal injury. In contrast, transplant‐related characteristics show limited independent influence. These findings support early risk stratification, careful therapeutic monitoring, and individualized immunosuppression to reduce renal complications during the initial post‐HCT period.