Clinical Utility of Serum sCD200/sCD200R Ratios in Predicting Current Activity of Antineutrophil Cytoplasmic Antibody-Associated Vasculitis

<b>Objectives</b>: 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). <b>Methods</b>: We included 70 patients with AAV in this pilot study, retrospectively reviewed their medical records, and collected clinical data at the time of AAV diagnosis. We also measured sCD200 and sCD200R in stored blood samples collected at diagnosis. In medical records, AAV activity at diagnosis had been assessed according to the Birmingham Vasculitis Activity Score (BVAS). The prediction potential of serum sCD200 and sCD200R concentrations and serum sCD200/sCD200R ratios for BVAS was evaluated using Pearson correlation analysis. <b>Results</b>: Among the 70 patients, the median age was 63.5 years, with 29 males and 41 females. Among the three CD200-related variables at diagnosis, serum sCD200/sCD200R ratios at diagnosis were significantly correlated with cross-sectional BVAS; however, serum sCD200 and sCD200R concentrations were not correlated with it. These results may indicate that serum sCD200/sCD200R ratios may better help predict cross-sectional AAV activity by increasing the range of opposing changes in the two variables. On the other hand, both serum sCD200 concentrations and serum sCD200/sCD200R ratios showed significant correlations with cross-sectional myeloperoxidase-ANCA titre, five-factor score, and serum creatinine levels at diagnosis. <b>Conclusions</b>: In this study, we demonstrated that serum sCD200/sCD200R ratios at diagnosis can be a useful and convenient biomarker to predict cross-sectional AAV activity calculated according to BVAS.