Objectives: A systemic inflammation response index (SIRI) has been recently introduced as a tool for the assessment of the prognosis of several critical medical conditions. In this study, we investigated whether SIRI at diagnosis could estimate the cross-sectional disease activity and predict poor prognosis during follow-up in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Methods: We reviewed the medical records of 224 immunosuppressive drug-naïve AAV patients and obtained clinical and laboratory data both at diagnosis and during follow-up. SIRI was calculated using the following equation: SIRI = peripheral blood neutrophil count × monocyte count/lymphocyte count. Results: The median age of AAV patients at diagnosis was 59.0 years and 33% were male. In the univariable linear regression analysis, SIRI value at diagnosis was not significantly correlated with the cross-sectional Birmingham vasculitis activity score (BVAS) (r = 0.125, P = 0.062). When the SIRI cut-off value at diagnosis was set at 2847.9 mm−3 using the receiver operator characteristic curve, the sensitivity was 56.0% and the specificity was 68.3% for all-cause mortality [area 0.618, 95% confidence interval (CI) 0.502, 0.734]. AAV patients with SIRI ≥ 2847.9 mm−3 had a significantly higher risk for all-cause mortality than those with SIRI < 2847.9 mm−3 [relative risk (RR) 2.747, 95% CI 1.181, 6.392]. During follow-up, AAV patients with SIRI ≥ 2847.9 mm−3 exhibited a significantly lower patients’ survival rate than those with SIRI < 2847.9 mm−3 (P = 0.003). Conclusions: SIRI at diagnosis could predict all-cause mortality during follow-up but it could not estimate the cross-sectional BVAS in AAV patients.
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