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

Abstract

Background: 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.

Methods: 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.

Results: 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.

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