Elevated Urinary IL-6 Predicts the Progression of IgA Nephropathy

Introduction: Immunoglobulin A nephropathy (IgAN) is the most common glomerulonephritis worldwide. However, biomarkers for predicting the progression or regression of IgAN remain a clinical challenge. In the present study, we aim to identify promising prognostic markers of IgAN. Methods: Using the cytokine antibody array, we detected serum and urinary levels of 9 common cytokines selected from 23 IgAN-related biomarkers in 32 patients with IgAN and 16 healthy controls. The best biomarkers for distinguishing IgAN patients from healthy controls were identified and confirmed in a multicenter cohort with 222 patients with IgAN and 159 age- and sex-matched healthy controls. Their associations with IgAN progression were further explored in 762 patients with IgAN with a median follow-up of 65 months. Results: Among the 9 candidate markers, urinary interleukin-6 (IL-6) and transforming growth factor-β1 (TGF-β1) levels were the best for distinguishing patients with IgAN from healthy controls. In the diagnostic cohort, both urinary IL-6 and TGF-β1 levels were elevated in patients with IgAN and showed good discriminatory power, with an area under curve (AUC) of 0.9725 (95% confidence interval: 0.9593-0.9858). Elevated urinary IL-6 level was independently and significantly correlated with the high risk of composite renal outcome (hazard ratio per log-transformed IL-6:1.420 [1.139-1.769]), but no statistical significance was observed between urinary TGF-β1 level and IgAN progression after adjusting for multiple confounders. Conclusions: Elevated urinary IL-6 and TGF-β1 levels predict the progression of IgAN. Urinary IL-6 is an independent risk factor and a promising noninvasive predictor for IgAN progression.