A multi-center cohort study evaluated hemoglobinuria as a marker of inflammation in IgA nephropathy.

INTRODUCTION: Hematuria is a hallmark clinical manifestation of IgA nephropathy (IgAN) and largely reflects underlying glomerular inflammation. Despite this, current guidelines prioritize proteinuria and estimated glomerular filtration rate for risk assessment, and the association between urinary findings and underlying histologic lesions remains incompletely characterized. METHODS: Here, we conducted a multicenter retrospective cohort study of patients with biopsy-proven IgAN (July 2015-July 2025) with concurrent urinalysis. Associations between hemoglobinuria (dipstick), hematuria (microscopy), proteinuria and individual Oxford Classification MEST-C components, and composite inflammatory lesions (M1, E1, and/or C1/C2; and E1 and/or C1/C2) were evaluated using unadjusted cohort-specific logistic regression models. Pooled odds ratios (ORs) were estimated using random-effects meta-analysis. RESULTS: Among 441 patients, hemoglobinuria was associated with M1 lesions (pooled OR 1.77, 95% CI 1.25-2.51), E1 lesions (1.75, 1.44-2.11), and crescentic lesions (1.57, 1.20-2.07). Hematuria was also associated with M1 lesions (1.24, 1.14-1.35), E1 lesions (1.22, 1.13-1.31), and C1/C2 lesions (1.18, 1.09-1.28). For the composite outcome (M1, E1, and/or C1/C2), pooled ORs were 2.28 (1.76-2.97) for hemoglobinuria, 1.36 (1.22-1.51) for hematuria, and 1.20 (1.04-1.38) for proteinuria. Hemoglobinuria and hematuria were not associated with chronic lesions, whereas proteinuria was consistently associated with T1/T2 lesions (1.35, 1.20-1.52). CONCLUSION: Dipstick hemoglobinuria is associated with histologic markers of active disease in IgAN and may provide clinically relevant information to complement current assessment of disease activity in IgAN.