To explore methods to improve the accuracy and efficiency of chemiluminescence immunoassay in the detection of treponema pallidum.

A retrospective collection of 496 013 outpatient and inpatient samples from January 2019 to December 2021 in 3 campuses of Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology was conducted. Primary screening test for syphilis antibodies used the chemiluminescence microparticle immunoassay (CMIA) and confirmation test used treponema pallidum particle agglutination (TPPA). Statistical analysis of the differences of the TPPA positivity rates in different years and the distribution of S/CO values of samples tested positive by the TPPA was performed by SPSS 23.0 software. The receiver operating characteristic curve (ROC) was used to determine the optimal S/CO value for the CMIA.

When grouped according to sample collection time, the positive rate of TPPA showed a decreasing trend year by year, but there was no statistically significant difference in TPPA positive rates among different years (χ²=4.847, P=0.089). Of the 496 013 cases tested by CMIA, 8696 were positive for syphilis antibodies. Among them, 6875 samples were confirmed as positive by TPPA, resulting in a false-positive rate of 0.37%, a positive predictive value of 79.06%, and a specificity of 99.63% for the CMIA initial screening test. According to the S/CO value, the positive samples tested by CMIA can be divided into 5 groups ranging from 1≤S/CO<2、2≤S/CO<3、3≤S/CO<4、4≤S/CO<18 and S/CO≥18. The positive predictive value of TPPA was 100% when S/CO≥18, and 95.81% when 4≤S/CO<18. The difference in positive predictive values between the 5 groups was statistically significant (χ²=3 825.005, P<0.05). When the S/CO=4.635, the area under the ROC curve was 0.923 9, the maximum Jorden index was 0.729 8, the sensitivity was 80.12%, the specificity was 92.86%, the positive likelihood ratio was 11.22, and the positive predictive value was 97.69%.

The number of syphilis infections has shown a decreasing trend year by year. The CMIA has a high specificity, but there are false positives. For samples 1≤S/CO<4.635 should be confirmed by TPPA to reduce the rate of misdiagnosis, and for samples with S/CO≥4.635, convenient and rapid syphilis-specific antibody assays such as colloidal gold can be used for review, and if the review is inconsistent, TPPA should be added to confirm the test, which can reduce the reporting cycle and improve the efficiency of the test. However, further evaluation is needed to determine whether this conclusion can be applied in clinical practice.