Objectives: This study investigated whether serum soluble CD200 (sCD200) and soluble receptor for CD200 (sCD200R) concentrations and serum sCD200/sCD200R ratios at diagnosis could predict cross-sectional activity in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Here, CD200 is linked to anti-neutrophil cytoplasmic antibody-associated vasculitis.