Systematic Review of Persistent Microscopic Hematuria and Kidney Outcomes in IgAN

Background: IgA nephropathy (IgAN) is a common glomerulonephritis, but the prognostic relevance of persistent microscopic hematuria remains uncertain. Persistent hematuria may reflect glomerular inflammation and complement proteinuria and estimated glomerular filtration rate (eGFR) in longitudinal assessment. We evaluated its association with kidney outcomes. Methods: MEDLINE, Embase, and Web of Science were searched through July 28, 2026, for studies evaluating longitudinal or persistent microscopic hematuria in IgAN. Categorical time-to-event estimates were pooled as hazard ratios (HRs) using random-effects models. Adjusted estimates were prioritized, and heterogeneity was assessed using the I 2 statistic and restricted maximum likelihood estimation. Continuous estimates were summarized because of heterogeneous definitions and scales. Results: A total of 9 reports representing 8 independent cohorts and 4776 participants were eligible. In the analysis including the Yu et al. cohort, 6 studies ( n = 3,031; 423 events) showed that persistent microhematuria was associated with kidney disease progression (HR: 2.64; 95% confidence interval [CI]: 2.00–3.47; I 2 = 0%). Results remained consistent after Hartung–Knapp adjustment (HR: 2.64; 95% CI: 2.25–3.09). An alternative analysis replacing Yu et al. with the updated Tang et al. cohort confirmed this association ( n = 3,469; 703 events; HR: 2.26; 95% CI: 1.54–3.31; I 2 = 26.5%), with similar Hartung–Knapp estimates (HR: 2.26; 95% CI: 1.53–3.33). Leave-one-out analyses showed that the findings were not driven by any single study. Continuous hematuria measures generally indicated higher kidney risk but were not pooled because of incompatible effect scales. Conclusions: Persistent microscopic hematuria is associated with kidney disease progression in IgAN. Longitudinal assessment may provide additional prognostic information alongside conventional biomarkers. Prospective studies should define its role in risk stratification and treatment monitoring.