Findings and significance of early follow-up biopsies after treatment of acute rejection in kidney transplant recipients.

Treatment resistant acute rejection after kidney transplantation is linked to inferior outcomes, yet many centers do not routinely perform follow-up biopsies. The optimal timing of such biopsies remains uncertain. We evaluated findings from follow-up biopsies performed ≤45 days after treatment of acute rejection and assessed their association with long-term outcomes. Adult kidney transplants performed from 01/2014 to 07/2024 were included (n = 2,420). Acute rejections were classified according to Banff criteria. T-cell-mediated rejection, including borderline TCMR changes, was treated with pulse steroids; antibody-mediated rejection was treated with steroids, intravenous immunoglobulin, and plasma exchange. Findings from follow-up biopsies taken ≤45 days after treatment of early acute rejection were correlated with graft outcomes. Of 383 patients (16%) with acute rejection within 3 months post-transplant, 221 underwent a follow-up biopsy ≤45 days. Of these, 50% were taken by protocol and 50% because of clinical reasons. In 164 cases (74%), rejection changes had resolved. At 1-year, median creatinine was 1.3 mg/dL in those without rejection, 1.6 mg/dL in patients with persistent changes, and 1.5 mg/dL in those with resolved changes. Persistent histologic rejection within 45 days was associated with inferior long-term graft survival.