Aims: Proteinuria is a strong prognostic factor in IgA nephropathy (IgAN). However, the risk threshold of proteinuria for kidney disease progression remains in debate. This study aimed to evaluate the risk of different levels of proteinuria on renal outcomes in Chinese patients with IgAN.
Materials and methods: Patients with biopsy-proven primary IgAN were recruited and divided into four groups based on their proteinuria levels: ≤ 0.30 g/d, 0.31 - 0.50 g/d, 0.51 - 1.00 g/d, and > 1.00 g/d. The primary outcomes were composed by doubling of baseline serum creatinine (Scr) and end-stage renal disease (ESRD, defined as eGFR < 15 mL/min/1.73m2, initiation of dialysis or transplantation).
Results: A total of 921 IgAN patients were enrolled in this study. During a median follow-up duration of 48 (34 - 62) months, higher risks of doubling of baseline Scr developed in patients with proteinuria 0.31 - 0.50 g/d (HR = 2.87, p = 0.04), 0.51 - 1.00 g/d (HR = 4.26, p = 0.002), and > 1.00 g/d (HR = 14.56, p < 0.001), while increased risks for ESRD were observed in patients with proteinuria 0.51 - 1.00 g/d (HR = 3.00, p = 0.02) and > 1.00 g/d (HR = 13.03, p < 0.001) in unadjusted Cox regression models. After adjusted for potential confounders, proteinuria 0.31 - 0.50 g/d (HR = 3.70, p = 0.04), 0.51 - 1.00 g/d (HR = 3.67, p = 0.02), and > 1.00 g/d (HR = 8.20, p < 0.001) remained to be significantly associated with higher risks of doubling of Scr, while only those with proteinuria > 1.00 g/d (HR = 6.04, p = 0.001) exhibited a markedly increased risk of ESRD.
Conclusion: Patients with proteinuria levels > 0.30 g/d already have a higher risk of doubling of baseline Scr, suggesting the necessity of early intervention in patients presenting with minimal proteinuria.