Delta Neutrophil Index Is Associated with Vasculitis Activity and Risk of Relapse in ANCA-Associated Vasculitis

PURPOSE: Delta neutrophil index (DNI) represents the immature granulocytes count associated with neutrophil-consumption. We investigated whether DNI might be associated with Birmingham vasculitis activity score (BVAS) at diagnosis and could predict relapse during the follow-up in patients with antineutrophil cytoplasmic antibody-associated vasculitis (AAV). MATERIALS AND METHODS: We reviewed the medical records of 97 patients having DNI results. Twenty patients had granulomatosis with polyangiitis (GPA), 58 had microscopic polyangiitis (MPA), and 19 had eosinophilic GPA (EGPA). We collected clinical and laboratory data including BVAS, five factor score (FFS), and DNI. The correlation coefficient and cumulative relapse free survival rate were obtained. The optimal cut-off of DNI was extrapolated by calculating the area under the receiver operator characteristic curve. RESULTS: DNI was significantly related to cross-sectional BVAS. Furthermore, among continuous variables, only DNI could reflect BVAS of GPA and MPA, but not EGPA. Severe AAV was defined as BVAS ≥20 (the highest quartile). At diagnosis, patients having DNI ≥0.65% had a significantly higher risk of severe GPA and MPA than those having not (relative risk 4.255) at diagnosis. During the follow-up, DNI ≥0.65% could predict the higher relapse rate. CONCLUSION: DNI could reflect BVAS at diagnosis and furthermore, DNI ≥0.65% could not only identify severe AAV at diagnosis, but also predict relapse during the follow-up in patients with GPA and MPA.