Urinary C4d and progression of kidney disease in IgA vasculitis

Background Immunoglobulin A (IgA) vasculitis nephritis (IgAVN) is the most common secondary IgA nephropathy (IgAN). Urinary C4d have been identified associated with the development and progression in primary IgAN; however, its role in kidney disease progression of IgAVN is still unclear.Methods This study enrolled 139 patients with IgAVN, 18 healthy subjects, 23 focal segmental glomerulosclerosis patients and 38 IgAN patients. Urinary C4d levels at kidney biopsy were measured using enzyme-linked immunosorbent assay. The association between urinary C4d/creatinine and kidney disease progression event, defined as 40% estimated glomerular filtration rate decline or end-stage kidney disease, was assessed using Cox proportional hazards models and restricted cubic splines.Results The levels of urinary C4d/creatinine (Cr) in IgAVN and IgAN patients were higher than in healthy controls. Higher levels of urinary C4d/Cr were associated with higher proteinuria and severe Oxford C lesions, and glomerular C4d deposition. After a median follow-up of 52.79 months, 18 (12.95%) participants reached composite kidney disease progression event. The risk of kidney disease progression event was higher with higher levels of Ln(urinary C4d/Cr). After adjustment for clinical data, higher levels of urinary C4d/Cr were associated with kidney disease progression in IgAVN [per Ln-transformed urinary C4d/Cr, hazard ratio 1.573, 95% confidence interval (CI) 1.101-2.245; P = .013]. Compared with the lower C4d/Cr group, the hazard ratio was 5.539 (95% CI 1.135-27.035; P = .034) for the higher levels group.Conclusions Higher levels of urinary C4d/Cr were associated with kidney disease progression event in patients with IgAVN.