The Banff 97 working classification of renal allograft pathology

Background. Standardization of renal allograft biopsy interpretation is nec essary to guide therapy and to establish an objective end point for clinica l trials. This manuscript describes a classification, Banff 97, developed b y investigators using the Banff Schema and the Collaborative Clinical Trial s in Transplantation (CCTT) modification for diagnosis of renal allograft p athology. Methods. Banff 97 grew from an international consensus discussion begun at Banff and continued via the Internet. This schema developed from (a) analys is of data using the Banff classification, (b) publication of and experienc e with the CCTT modification, (c) international conferences, and (d) data f rom recent studies on impact of vasculitis on transplant outcome. Results. Semiquantitative lesion scoring continues to focus on tubulitis an d arteritis but includes a minimum threshold for interstitial inflammation. Banff 97 defines "types" of acute/active rejection. Type I is tubulointers titial rejection without arteritis. Type II is vascular rejection with inti mal arteritis, and type III is severe rejection with transmural arterial ch anges. Biopsies with only mild inflammation are graded as "borderline/suspi cious for rejection." Chronic/sclerosing allograft changes are graded based on severity of tubular atrophy and interstitial fibrosis. Antibody-mediate d rejection, hyperacute or accelerated acute in presentation, is also categ orized, as are other significant allograft findings. Conclusions. The Banff 97 working classification refines earlier schemas an d represents input from two classifications most widely used in clinical re jection trials and in clinical practice worldwide. Major changes include th e following: rejection with vasculitis is separated from tubulointerstitial rejection; severe rejection requires transmural changes in arteries; "bord erline" rejection can only be interpreted in a clinical context; antibody-m ediated rejection is further defined, and lesion scoring focuses on most se verely involved structures. Criteria for specimen adequacy have also been m odified. Banff 97 represents a significant refinement of allograft assessme nt, developed via international consensus discussions.