Analysis of grey area of Treponema pallidum specific antibody detection
ZHAO Jing BIAN Chengrong LI Boan WANG Han
Clinical Laboratory Medical Center, the Fifth Medical Center, General Hospital of PLA, Military Clinical Laboratory Diagnostic Center for Infectious Diseases, Beijing 100039, China
Abstract:Objective To investigate the grey area of Treponema pallidum specific antibody detected by chemiluminescent immunoassay, and improve the validity and accuracy of syphilis laboratory diagnosis. Methods The patients with cut-off (S/CO) value 1 to 9 (assumed grey area) of Treponema pallidum specific antibody detected by chemiluminescent immunoassay from February 2016 to May 2018 were collected from the Fifth Medical Center in General Hospital of PLA. The false positive rate of chemiluminescent immunoassay in grey area was evaluated by using the methods of reverse detection process of syphilis laboratory and the results of immunoblotting as gold standard. Results A total of 25 190 cases were detected by chemiluminescent immunoassay, and 462 cases (1.83%) were observed within grey area. The false positive rate was 0.74% in 234 cases with S/CO values ranging from 1 to 3, 0.27% in 109 patients with S/CO values ranging from greater than 3 to 6, and 0.12% in 119 patients with S/CO values ranging from greater than 6 to 9. There was a significant difference among three groups (P < 0.05). Comparison of S/CO values in greater than 6 to 9 patients with lower false positive rate, the false positive rate of S/CO value greater than 6 to 7 was 0.072%, the false positive rate of S/CO value greater than 7 to 8 was 0.024%, the false positive rate of S/CO value greater than 8 to 9 was 0.020%, and the difference between three groups was statistically significant (P < 0.05). Conclusion In the assumed grey area, when the specific antibody of Treponema pallidum is detected by chemiluminescent immunoassay, the false positive rate showes a decreasing trend with the increase of S/CO value. The gray area should be set to S/CO value of 1 to 7.