Objective To evaluate the utility of the gray zone results of syphilis-specific antibody detection by chemiluminescent microparticle immunoassay(CMIA)with S/CO values of 1-10 in routine screening for syphilis infection.Methods A total of 119 907 patients who underwent CMIA for syphilis in the hospital were retrospectively analyzed.Among them,602 patients with S/CO values of 1-10 in the evaluation results ob-tained with CMIA method for two times were included in the study.Treponema pallidum particle agglutina-tion(TPPA)test was adopted as the confirmatory test and rapid plasma reagin(RPR)was performed to as-sess the disease activity.The patients were divided into three groups(CMIA method S/CO 1-3 group 399 ca-ses,CMIA method S/CO＞3-6 group 136 cases,CMIA method S/CO＞6-10 group 67 cases)according to different intervals of S/CO values obtained with CMIA method.Then the patients were divided into two groups(0-3 years old group 399 cases,＞3 years old group 136 cases)according to their ages.The general da-ta and test results of the patients were compared between groups to analyze the differences.Results Among 119 907 patients with syphilis CMIA detection,a total of 602 cases with S/CO values of 1-10 were confirmed in the two initial screening results with CMIA method and the positive detection rate was 5.02‰.Among them,in TPPA retest,the number of cases with positive results was 186(30.9％)and 16 cases(2.7％)were suspected to be weak positive.In RPR test,the number of cases with positive was 7(1.20％).In the grouping statistics based on S/CO values of CMIA method,the positive rate of CMIA method S/CO 1-3 group in TP-PA retest was significantly lower than that of CMIA method S/CO＞3-6 group and CMIA method S/CO＞6-10 group(P＜0.05).The RPR positive rate also showed CMIA method S/CO 1-3 group significantly lower CMIA method S/CO＞6-10 group(0.3％vs.3,4.5％,P＜0.05).The S/CO of CMIA in 0-3 years old group were lower than those in＞3 years old group[1.53(1.27,2.24)vs.2.30(1.48,4.15),P＜0.05],and the positive rate of TPPA in 0-3 years old group was lower than that in＞3 years old group[0.7％vs.40.0％,P＜0.05].Conclusion The specificity of routine screening of syphilis-specific antibody in CMIA method S/CO 1-3 group is low,so TPPA is recommended to assist diagnosis.In CMIA method S/CO＞6-10 group,more than 10.0％false positives are still confirmed by TPPA reexamination,so it is suggested that the TPPA reexamination cut-off value should be 10.0-3 years old group CMIA method S/CO value is low,the TPPA positive rate is low.