Abstract:

Objective To establish a reasonable positive cut off value of anti-treponema pallidum (TP) antibody in pregnant women by chemiluminescence immunoassay(CLIA).Methods A total of 13 974 serum samples from pregnant women for anti-TP antibody were collected. All the samples were determined by Kemei Dongya Chemclin CLIA system. The positive samples [signal-to-cut off (S/CO) ratio≥1.0] were further verified by western blotting (WB). The performance was evaluated by receiver operating characteristic (ROC) curve. Results The 152 samples of S/CO ratio≥1.0 were determined by Chemclin CLIA system. The screening positive reaction rate was 1.09%. The results verified by WB for the screening positive samples showed that 119 samples were positive, 7 samples were indeterminate,and 26 samples were negative. The false positive rate of screening positive reaction samples was 17.11% . The ROC curve indicated that the S/CO ratio for anti-TP antibody was 3.32 when Youden index reached maximum. The S/CO ratio was 3.25, when positive predictive value was ≥95% of Chemclin CLIA system. Conclusions In order to both reduce the false positive rate of anti-TP antibody screening and minimize the number of samples to be further determined by confirmation assay,each laboratory should set up a suitable S/CO ratio for different populations and determination systems (reagents) and determine the S/CO ratio scope to be further determined by confirmation assay.

Key words: Anti-treponema pallidum antibody, Chemiluminescence immunoassay, Confirmation assay, Positive predictive value, Pregnant woman