The relationship of untreated borderline infiltrates by the Banff criteria to acute rejection in renal allograft biopsies.

The relationship of borderline infiltrates to acute rejection by Banff criteria in renal allografts of patients receiving only maintenance immunosuppression is not clear. Renal allograft biopsies with borderline lesions that were not treated with additional anti-rejection therapy were retrospectively studied. Sixty-five such biopsies were identified from 50 patients, and their outcome was determined by serum creatinine and/or histologic findings in subsequent biopsies, up to 40 d after the initial biopsy. In addition to the borderline infiltrates, there was evidence of acute cyclosporine or tacrolimus toxicity (58%), acute tubular necrosis (12%), and urinary obstruction (12%). Forty-day follow-up after 30 (46%) biopsies revealed serum creatinine < 110% of baseline, and repeat biopsies were not indicated. In 17 (26%), the serum creatinine initially decreased, then increased, and follow-up biopsies showed acute rejection in nine. In 18 (28%), the creatinine remained elevated and follow-up biopsies revealed acute rejection in nine. The untreated borderline infiltrates were thus nonprogressive after 47 biopsies (72%) and progressed to histologic acute rejection after 18 (28%). When there was increasing or persistently elevated creatinine after the initial biopsy, 51% of cases (18 of 35) progressed to acute rejection. Infiltrates that progressed to rejection had more frequent glomerulitis (7 of 18 versus 3 of 47, P = 0.003) and Banff acute score indices (i+t+v+g) >2 (16 of 18 versus 29 of 47, P = 0.03). A majority (72%) of borderline infiltrates not given additional anti-rejection therapy did not progress to acute rejection over 40 d of follow-up, suggesting that conservative management of these lesions, at least in the short term, may be more appropriate than routine treatment as acute rejection.