Preferable procedure for the screening of syphilis in clinical laboratories in China

Background: With the rapid expansion of infectious syphilis all over the world, optimal procedures for screening syphilis are urgently required. Conventional methods for the diagnosis of syphilis are time- and labor-consuming. We compared automated chemiluminescent micro-particle immunoassay (CLIA) with conventional methods to verify whether CLIA is feasible for syphilis screening. Methods: A cross-sectional assay was conducted on 3962 serum samples tested by CLIA, rapid plasma reagin test (RPR), and Treponema pallidum particle agglutination (TPPA). Meanwhile, another 36 000 sera were screened for syphilis using CLIA and the positive samples were confirmed using TPPA, RPR or Western blotting. Results: The sensitivity and specificity were 100% and 99.8% for CLIA, and 65% and 99.6% for RPR. With the elevation of the optical density value of samples to cut-off ratio (S/CO) value, the true-positive rate of CLIA increased significantly, and when the S/CO value exceeded 10, the true-positive rate of CLIA reached 100%. The false-positive rate of CLIA was 0.22%; pregnant women had the most false-positive results, followed by elderly people and cancer patients. Conclusion: CLIA is suggested as a screening test for the diagnosis of syphilis, while TPPA and RPR are required for confirming the positive samples and monitoring their activity.