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 < 15 mm³ (relative risk 2.596). However, in the multivariable linear and logistic regression analyses, LUC did not seem to estimate the current BVAS independently among clinical and laboratory variables. Conclusion: LUC count was significantly correlated with the current BVAS and LUC count ≥ 15 mm³ could estimate the current high BVAS in patients with ANCA positive AAV.