Abstract

To set up arbitrary cutoff values and to determine whether arbitrary cutoff values can be predictive of confirmed positive results by compare cutoff index (COI) values of the borderline or initially reactive samples (0.9≤COI<7.0) with HBsAg confirmation test. 238 HBsAg borderline or initially reactive sera or plasma with 0.9≤COI<7.0 were collected from the clinical patients in West China Hospital of Sichuan University. Each sample must be re-determined in duplicate with Elecsys HBsAg II assay according to manufacturers’ instructions. All repeated reactive samples were confirmed with HBsAg neutralization assay. HBV viral loads were tested if necessary. 116 out of 238 (48.7%) samples, deemed as weakly reactive (WR) samples, were found COIs <2.0. 12.1% (11 out of 91) of WR samples did not pass confirmation in repeated reactive samples. Statistical analysis indicated that much more WR samples were found in HBsAg negative group (100%) than those in repeatedly reactive group (42.7%) (P<0.05). In the 116 WR samples (COI<2.0), 25 samples were HBsAg negative and 11 did not pass the neutralization. 36 WR samples were discovered electrochemiluminescence immunoassay HBsAg negative or confirmed negative. Furthermore, four HBsAg negative and one confirmed negative samples were found HBV DNA existed. 36 WR samples harbored with anti-HBc and anti-Hbe. By setting up modified cutoff values to 1.455 or 1.785, the positive predicted value (PPV) could be improved from 95.2 to 99.4% or 100% in this study. Evaluation of HBsAg prevalence through Elecsys HBsAg II overestimated the true positive, especially in WR samples.Adjusted COIs decreased the need of HBsAg neutralization test, to same degree.

Key words: hepatitis B surface antigen (HBsAg), confirmation test,Electrochemiluminescence immunoassay (ECLIA), weakly reactive.