Hepatitis B surface antigen confirmatory testing for diagnosis of hepatitis B virus infection in Taiwan

This study aimed to examine the application of hepatitis B surface antigen (HBsAg) confirmatory testing when diagnosing hepatitis B infection among young persons in Taiwan with a low prevalence rate of hepatitis B infection. HBsAg status, the presence of antibodies against HBsAg (anti-HBs), and the presence of antibodies against hepatitis B core antigen (anti-HBc) were compared among 403 graduate students (mean age 22.8 ± 0.7 years) and 1,745 undergraduate students (18.6 ± 1.0 years) from one university, and 367 adult subjects (41.1 ± 15.8 years) in 2008. Any HBsAg-positive subjects were tested with an HBsAg confirmatory test. Chi-square tests for trend and predictive values of positivity (PVP) when using HBsAg-positive only for determining confirmed cases of hepatitis B infection were compared across the three cohorts. The prevalence of HBsAg positivity among subjects decreased from 16.3% in the adults to 5.2% in the graduate students and then to 2.8% for the undergraduate students (P = 0.0007). The PVP of HBsAg testing when determining cases of hepatitis B decreased from 0.97 for the adults to 0.81 for the graduate students and then to 0.56 for the undergraduate students (P < 0.0001). Thus, a significant decrease in the true-positive rate of HBsAg among the students born after the introduction of hepatitis B vaccination was observed only when HBsAg testing was applied. Additional neutralization tests may therefore become mandatory for persons with a positive HBsAg test result who were born after the commencement of the universal neonatal hepatitis B vaccination program in Taiwan.