International standardization of criteria for histologic diagnosis of chronic rejection in renal allografts.

An accurate diagnosis of acute rejection in renal allografts can be made histologically by quantitating specific morphologic changes observed on biopsy. The Banff Schema, an internationally standardized system of renal allograft biopsy assessment published in the August 1993 issue of Kidney International (1) has been shown to be highly reproducible and clinically valid for acute rejection. The schema also includes quantitation of the lesions of chronic rejection: fibrous intimal thickening, chronic transplant glomerulopathy, interstitial fibrosis, tubular atrophy. Biopsies that demonstrate these lesions are assigned the noncommittal term "chronic transplant nephropathy," as other conditions such as cyclosporine toxicity, hypertension, infection, and reflux can generate these lesions as well. In certain clinical settings, some lesions probably are specific for chronic rejection, such as fibrous intimal thickening with fragmentation of the elastic lamina, but because of their extreme focality they are infrequently seen on biopsy. It is possible that chronic rejection involves a specific pattern of scarring and peritubular capillary injury, but these changes have yet to be fully characterized. Late allograft biopsies in ongoing clinical trials of new immunosuppressive agents will help to further define the specific pathologic changes of chronic rejection.