Predicting renal outcome in IgA nephropathy.

Immunoglobulin A (IgA) nephropathy, the most common form of glomerulonephritis worldwide, is characterized by a heterogeneous clinical course. In this study, multivariate analysis was performed to identify histopathologic and clinical features that most accurately predict adverse outcome from a dataset of 148 individuals with IgA nephropathy who underwent renal biopsy at our institution between 1973 and 1995. A semiquantitative scoring system was developed for assessment of six glomerular, eight interstitial, and six vascular histopathologic features of IgA nephropathy. Glomerular and interstitial proliferative activity was evaluated by immunostaining archival biopsy specimens with Mib-1, an antibody directed against the Ki-67 antigen. Kaplan-Meier survival analysis was performed, with renal failure being defined as onset of dialysis or transplantation. A number of clinicopathologic factors were univariately associated with adverse outcome, including elevated serum creatinine levels; the presence of hypertension; proteinuria; component and total histopathologic scores; and positive glomerular or interstitial Mib-1 scores. The total glomerular score, consisting of the arithmetic sum of each of the six component scores, was the strongest histopathologic predictor of adverse outcome. Total interstitial and vascular scores also provided more prognostic information than did individual component scores. By multivariate analysis, high total glomerular scores, increased serum creatinine levels at diagnosis, and younger age were significant (P < 0.01) independent predictors of renal failure. Our studies provide a rational basis for the inclusion of composite histopathologic scores in clinical intervention studies of patients with IgA nephropathy and other glomerular disorders.