Moran S, Scott J, Clarkson M, et al. - In renal vasculitis flare, increased urinary soluble CD163 (sCD163) (area under the curve 0.95 with a cutoff of 250 ng/mmol) was detected whereas it remained low in flare mimics. An elevation in urinary sCD163, in the absence of glomerular macrophage infiltration, was shown to be caused by nonspecific protein leakage in nephrotic syndrome, leading to false-positive results; this can be rectified with urine protein normalization.

• Participants included cohorts with ANCA-associated vasculitis (AAV) patients (with or without proteinuria) and healthy and non-AAV disease controls, patients with potential renal vasculitis flare, and patients with podocytopathy.

• A diagnostic-grade urinary sCD163 assay was evaluated in these cohorts.

• A diagnostic reference range was established, with a cutoff of 250 ng/mmol for active renal vasculitis (AUC, 0.978).

• In AAV cases with nephrotic-range proteinuria and in primary podocytopathy, reduction in urinary sCD163's specificity was evident, with 62% of nephrotic patients showing a "positive" urinary sCD163.

• The greatest clinical utility for active renal vasculitis diagnosis was afforded by urinary sCD163 normalization to total urine protein rather than creatinine, in AAV cases with significant proteinuria.