Prognostic factors of IgA nephropathy presenting with mild proteinuria at the time of diagnosis (a multicenter cohort study)

BACKGROUND: Clinical factors affecting renal prognosis in patients with immunoglobulin A nephropathy (IgAN) and low urinary protein excretion (U-Prot) remain unclear. This study evaluated such factors in patients with clinical grade I (CG-I) IgAN with U-Prot < 0.5 g/day. METHODS: This secondary analysis of a previous retrospective study included 394 patients with CG-I IgAN. The primary outcome was the first occurrence of a 1.5-fold increase in serum creatinine levels from baseline. Factors related to renal prognosis were examined using univariate and multivariate Cox regression analyses. CG-I was divided into C-Grade Ia (CG-Ia) (n = 330) with baseline eGFR ≥ 60 ml/min/1.73 m(2), and C-Grade Ib (CG-Ib) (n = 64) with baseline eGFR < 60 ml/min/1.73 m(2). Outcome incidence was compared between conservative and aggressive therapy (corticosteroids and/or tonsillectomy) groups. RESULTS: Overall outcome incidence was significantly higher in CG-Ib than in CG-Ia; the cumulative incidence was significantly higher in CG-Ib (hazard ratio, 9.67; 95% confidence interval, 2.90–32.23). Older age, higher IgA levels, eGFR < 60 mL/min/1.73 m(2), lower eGFR at baseline were independent prognostic factors for CG-I. Older age, lower eGFR, higher IgA levels at baseline, and U-Prot remission at 1-year post-diagnosis were independent prognostic factors for CG-Ib. Aggressive therapy tended to suppress the cumulative outcome incidence compared with conservative therapy in CG-Ib (p = 0.087). CONCLUSION: An eGFR < 60 mL/min/1.73 m(2) is a significant predictor of renal prognosis in patients with IgAN and U-Prot < 0.5 g/day. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10157-023-02316-2.