A scoring system to predict renal outcome in IgA nephropathy: from a nationwide prospective study

Background. Immunoglobulin A (IgA) nephropathy is the most common form of glomerulonephritis in the world, and a substantial number of patients develop end-stage renal disease (ESRD). Although there are several prognostic indicators, it remains difficult to predict the renal outcome in individual patients. Methods. A prospective cohort study was conducted in 97 clinical units in Japan from 1995 to 2002. We analysed the data from 2269 patients using proportional hazards models in order to determine the predictors of ESRD in IgA nephropathy and to develop a scoring system to estimate ESRD risk. Results. During the follow-up (median, 77 months), 207 patients developed ESRD. Systolic hypertension, proteinuria, hypoproteinaemia, azotaemia and a high histological grade at initial renal biopsy were independently associated with the risk of ESRD. Mild haematuria predisposed patients to ESRD more than severe haematuria. A scoring system was developed to estimate the 7-year ESRD risk from eight clinical and pathological variables. Actually, this prognostic score accurately classified patients by risk: patients with estimates of 0.0-0.9, 1.0-4.9, 5.0-19.9, 20.0-49.9, and 50.0-100.0% had a 0.2, 2.4, 12.2, 40.2 and 80.8% of ESRD incidence over 7 years, respectively. The corresponding area under the receiver operating characteristic curve was 0.939 [95% confidence interval (CI), 0.921-0.958]. This score was verified in repetitions of the derivation-validation technique. Conclusions. Although the quality of some data collected by the mail survey is limited and the influence of therapy could not be considered, this scoring system will serve as a useful prognostic tool for IgA nephropathy in clinical practice.