Abstract:

Objective To investigate the retesting range of ani-treponema pallidum (TP) antibody determined by chemiluminescence microparticle immunoassay (CMIA) and improve the retesting procedure.Methods A total of 21 894 serum samples were screened by CMIA, the positive samples were retested duplicately by the same reagent kit of the same lot number and confirmed by western blotting (WB). The detection results were classifed into several groups for further analysis according to signal-to-cut off (S/CO) ratios. Results In 21 894 serum samples, 630 cases were positive by CMIA. The samples were classified into 7 groups according to S/CO ratios:1.0-2.0, 2.1-4.0, 4.1-6.0, 6.1-8.0, 8.1-9.0, 9.1-10.0 and>10.1. The retesting coincidence rates by CMIA were 62.5%(40/64), 80.0%(60/75), 93.9%(77/82), 100.0%(94/94), 100.0%(85/85), 100.0%(50/50)and 100.0%(180/180).The coincidence rates for retesting by WB and CMIA were 35.0%(14/40), 46.7%(28/60),75.3%(58/77), 81.9%(77/94), 88.2%(75/85), 96.0%(48/50) and 98.8%(178/180). Conclusions The S/CO ratio for retesting range by CMIA for the determination of anti-TP antibody is considered appropriate from 1.0-8.0 under a standardized laboratory condition and positive predictive value≥95% . Reports can be sent directly with S/CO ratio≥8.1. WB should be employed to confirmation assay with 1.0≤S/CO ratio ≤8.0. The appropriate retesting range not only can assure the accuracy of testing results, but also can reduce the sample numbers of confirmation assay.

Key words: Ani-treponema pallidum antibody, Retesting, Range, Chemiluminescence microparticle immunoassay, Western blotting