Objective:To analyze clinical significance of peripheral blood neutrophil CD64(nCD64)index in patients with anti-neutrophil cytoplasmic antibody(ANCA)-associated vasculitis(AAV).Methods:The clinical data of 98 AAV patients admitted to the First Medical Center of Chinese People's Liberation Army General Hospital from February 1,2023 to February 29,2024 were retrospectively selected,and they were divided into the high-value group(nCD64 index＞1.82,28 patients)and the normal-value group(nCD64 index≤1.82,70 patients)based on the nCD64 index.Ethylenediaminetetraacetic acid(EDTA)-anticoagulated venous blood specimens were collected from patients in both groups,and the mean fluorescence intensity of CD64 expression on the surfaces of polymorphonuclear leukocytes(PMN),lymphocytes(Lym)and monocytes(Mo)was detected by flow cytometry.Clinical manifestations,relevant examination data of hospital,and survival situation of patients with regular follow-up were compared between the two groups.Results:Spearman correlation analysis showed that peripheral blood nCD64 index was positively correlated with Birmingham vasculitis activity score(BVAS)in AAV patients(r=0.216,P＜0.05).There were no statistically significant differences in white blood cells(109/L),blood creatinine(μmol/L),CD8+lymphocytes(amount/μl),CD3-CD16+CD56+lymphocytes(amount/μl),blood sedimentation and interleukin 6 between the two groups.The mean values of BVAS,neutrophils(109/L),CD8+CD28-lymphocytes(％)were respectively(14.96±8.62),(7.51±4.56),(22.16±13.28)in high-value group,which were significantly higher than those[(11.88±7.39),(6.32±3.60)and(17.32±11.27)]in normal-value group,and the mean values of lymphocytes(109/L),platelets(109/L),hemoglobin(g/L),CD3+lymphocytes(amount/Al),CD4+lymphocytes(amount/μl),CD8+CD28+lymphocytes(％)were respectively(1.52±1.01),(216.84±92.32),(106.26±21.99),(1401.15±658.22),(618.43±420.50)and(12.43±5.98)in high-value group,which were significantly lower than those[(1.98±0.95),(248.20±97.21),(114.30±24.71),(1815.43±657.29),(969.15±385.72)and(15.77±7.66)]in normal-value group,and the differences of them between two groups were statistically significant(t=-2.68,-2.04,-2.54,3.25,2.26,2.34,2.02,2.84,3.02,P＜0.05),respectively.Neutrophil/lymphocyte ratio and C-reactive protein of high-value group were higher than those of normal-value group,and eosinophils of high-value group were lower than that of normal-value group,and the differences of them between two groups were statistically significant(Z=-3.370,-2.396,-4.462,P＜0.05),respectively.Conclusions:Peripheral blood nCD64 index is positively correlated with BVAS in AAV patients,which involve in multiple immune cells and inflammatory factors.It has clinically application value in monitoring the disease progression and assessing the prognosis.