Abstract: Objective To investigate the diagnostic significance of combined detection of NAP,PCT and CRP in orthopedic postoperative infection. Method sThree hundred and four inpatients who had received Class Ⅱ treatments were divided into infection group （262 cases） and non-infection group （42 cases） from June 2016 to January 2018. 5 mL of venous blood was collected on the first day postoperation. PCT was detected by double-antibody sandwich immunochemiluminescence assay,CRP was tested by immunofluorescence dry-quantitative assay,and NAP assay was carried out with NAP substrate-AMP buffer method. Antibiotic sensitive tests were performed with disc diffusion assay （K-B method）. The ROC curves were analyzed according to the expression levels of NAP,PCT and CRP. Results Among 304 orthopedic patients,42 （13.8%） had postoperative infections,from whom 89 strains of bacteria were isolated that included 39 （43.8%） G-positive and 37 （41.6%） G-negative bacteria,4 （4.5%） viruses,6 （6.7%） mycoplasma,and 3 （3.4%） unidentified microbes. The infection group was significantly higher than the non-infection group in terms of NAP scores,NAP positive rate,PCT and CRP （P<0.05）. The combined detections of NAP,PCT,and CRP for postoperative orthopedic infection was AUC：0.928,which was significantly higher than that of NAP,PCT,and CRP （AUC：0.667,0.779,0.877,P<0.01）,suggesting that joint detections of NAP,PCT,and CRP help with the diagnosis in orthopedics postoperative infection. Conclusion Combined detections of NAP,PCT and CRP are clinically valuable in the diagnosis of orthopedic postoperative infection.

Key words: Orthopedics, infection, Neutrophil, alkaline, phosphatase, Procalcitonin, C-reactive, protein