IgA nephropathy: prognostic classification of end-stage renal failure. L'Association des Néphrologues de l'Est

As yet, no clinical or morphological prognostic classification of IgA nephropathy (IgAN) has been generally accepted. The objective of our study was to quantify the risk of developing end-stage renal failure (ESRF) in IgAN.

We report a prospective longitudinal study of 210 patients with IgAN confirmed by biopsy between 1987 and 1991. Thirty-two (15.2%) patients were lost to follow-up. Mean follow-up after renal biopsy was 5.6 (SD = 2.6) years. The variables included age, gender, illnesses prior to discovery of IgAN, clinical features at IgAN discovery, 24-h proteinuria, serum creatinine, IgA level, and antihypertensive drugs taken at the time of renal biopsy. Sixty-six renal biopsies were classified by light-microscopy according to Lee's morphological classification. The end-point was ESRF. Survival was analysed by a backward and forward stepwise procedure using the Cox model. The most accurate determination of relative risk was obtained by assessing collinearity of the variables.

Thirty-three patients (15.7%) (31 men) developed ESRF. The five univariately significant variables: gender, gross haematuria, 24-h proteinuria (24-P), serum creatinine (SC), and antihypertensive treatment, were candidates for multivariate analysis. The final model used SC (< or = 100, 100-150, > 150 mumol/l), 24-P (< 1, > or = 1 g/day) and gender (female vs male) as independent variables (relative risk and 95% confidence interval were 3.5 (2.1, 5.9) for SC; 5.1 (1.9, 13.6) for 24-P; and 3.5 (0.9, 15) for gender). These estimates were used to construct a prognostic classification of ERSF for men with IgAN: stage 1 (SC < or = 150 mumol/l and 24-P < 1 g/day), stage 2 ((SC > 150 mumol/l and 24-P < 1 g/day) or (SC < or = 150 mumol/l and 24-P > or = 1 g/day)); stage 3 (SC > 150 mumol/l and 24-P > or = 1 g/day). The ESRF-free survival was estimated with Kaplan-Meier analysis. It was 98.5% for stage 1, 86.6% for stage 2, 21.3% for stage 3 (P < 0.001), 7 years after histological diagnosis. The validity of Lee's prognostic classification was confirmed using an independent sample.

These classifications identify groups at high risk of ESRF. Therapeutic studies should focus on these groups.