A scoring system to predict renal outcome in IgA nephropathy: a nationwide 10-year prospective cohort study

Background. Immunoglobulin A nephropathy (IgAN) is the most common form of glomerulonephritis, and a substantial number of patients succumb to end-stage renal disease (ESRD). However, prediction of the renal outcome in individual patients remains difficult. We have already published a scoring system using the data in a prospective cohort of IgAN patients followed up from 1995 to 2002. Methods. The cohort was further followed up until 2005 in 97 clinical units in Japan. The data from 2283 patients were analysed by Cox regression to determine the predictors of ESRD in IgAN, and their beta-coefficients were converted into scores to estimate ESRD risk within 10 years. Results. During the follow-up (median, 87 months), 252 patients developed ESRD. Male sex, age less than 30 years, family histories of chronic renal failure and chronic glomerulonephritis, hypertension, proteinuria, mild haematuria, hypoalbuminaemia, low glomerular filtration rate and a high histological grade at initial renal biopsy were associated with the risk of ESRD in the multivariable analysis. A scoring system was framed to estimate the 10-year ESRD risk using eight variables significant in both univariable and multivariable models. This prognostic score accurately classified patients by risk: patients with estimates of 0-4.9, 5.0-19.9, 20.0-49.9 and 50.0-100% had an observed incidence of 1.7, 8.3, 36.7 and 85.5%, respectively. The corresponding area under the receiver-operating characteristic curve was 0.942 (95% confidence interval, 0.925-0.958). Conclusion. This validated scoring system to quantitatively estimate ESRD risk during the 10-year follow-up of IgAN patients will serve as a useful prognostic tool in clinical practice.