Clinical significance of large unstained cell count in estimating the current activity of antineutrophil cytoplasmic antibody‐associated vasculitis

Background We investigated whether large unstained cell (LUC) count could estimate the current high activity according to Birmingham vasculitis activity score (BVAS) in patients with antineutrophil cytoplasmic antibody (ANCA) positive ANCA‐associated vasculitis (AAV). Methods We retrospectively reviewed the medical records of 176 immunosuppressive drug‐naïve patients with ANCA positive AAV. Clinical and laboratory data at diagnosis, including LUC count, were collected. High BVAS was defined as the highest tertile of BVAS (BVAS ≥ 15) in this study. Results The median age was 61.0 years, and 64.8% were female. The median LUC count was 60.0 mm3, and LUC was detected in 106 patients. LUC count was significantly correlated with BVAS, age, white blood cell count, haemoglobin, platelet count, serum albumin, erythrocyte sedimentation rate and C‐reactive protein. Overall, the median BVAS in AAV patients with LUC positivity was significantly higher than that in those without (14.0 vs 10.0). When the cut‐off of LUC count for the current high BVAS was set as BVAS ≥ 15 mm3, AAV patients with LUC count ≥ 15 mm3 had a significantly higher risk for the current high BVAS than those with LUC count