Abstract: Objective To investigate the diagnostic value of neutrophil CD64 index in bacterial infections of acute exacerbations of chronic obstructive pulmonary disease(AECOPD). Methods The investigation enrolled 50 patients with chronic obstructive pulmonary disease(COPD),among whom 10 with stable COPD,16 with nonbacterial infections AECOPD and 24 with bacterial infections AECOPD.For all COPD patients,the white blood cell count(WBC),erythrocyte sedimentation rate(ESR),c-reactive protein(CRP),procalcitonin(PCT) and neutrophil CD64 index were measured and compared between the three groups.The receiver operating characteristic(ROC) curves were estimated.The areas under ROC curves(AUC) were compared by z-test,and the optimal cut-off values for diagnosis were determined. Results The WBC,ESR,CRP,PCT and neutrophil CD64 index in three groups were significantly different.The ROC curves of the WBC,ESR,CRP,PCT and neutrophil CD64 index for diagnosing bacteria infections of AECOPD were estimated,and their AUC were 0.779,0.750,0.772,0.885,0.929,respectively.The AUC of neutrophil CD64 index was significantly larger than these of WBC,ESR or CRP(P<0.05),while larger than that of PCT,but there was no statistical difference between the both(P>0.05).With the cutoff value of 2.35,the sensitivity and specificity of neutrophil CD64 index for diagnosis were 87.5% and 84.6%. Conclusion The Neutrophil CD64 index as a inflammatory biomarker,was available for diagnosis of bacterial infections of AECOPD.