Efficient implementation of hepatitis B surface antigen confirmatory neutralization tests

Introduction: To prevent misreporting of false positives in the hepatitis B surface antigen (HBsAg) assay, it is recommended to confirm the low-positive cases with neutralization tests. However, currently not many facilities are implementing this due to the additional cost. The aim of this study was to clarify the risk factors for false positives in the high-sensitivity HBsAg quantitative tests to reduce the neutralization tests. Methods: In this retrospective cohort study, we analyzed 47,305 patients who had their HBsAg value measured at Sapporo Medical University Hospital between November 2016 and March 2022. The patients eligible for the neutralization tests were those with HBsAg values between 0.005 and 1.000, even after reexamination by highspeed centrifugation. Results: HBsAg quantitative tests were performed in 71,475 tests. Of these, 817 tests and 376 patients were subjected to neutralization tests. Of the patients who met the criteria, 329 were included in this study. Fifty-seven cases (17%) had negative results in the neutralization tests, suggesting false positives for the HBsAg assay. Multivariate analysis showed that younger age (adjusted odds ratio [aOR] 6.57), female sex (aOR 2.32), lower HBsAg values (aOR 59.6), and reagent improvement (aOR 2.06) were independent risk factors for false positives. The false-positive rate was actually high at 33.1% in the HBsAg range of 0.005-0.049 IU/mL and at 1.2% in the range above 0.050 IU/mL. Conclusions: Confirmatory neutralization tests should be performed at least in the range of 0.005-0.049 IU/mL where quantification is possible with a higher-sensitivity assay.

Automated summary

The aim of this study was to identify the risk factors for false positives in high-sensitivity HBsAg quantitative tests and reduce the need for neutralization tests. The results showed that younger age, female sex, lower HBsAg values, and reagent improvement were independent risk factors for false positives. The false-positive rate was highest in the range of 0.005-0.049 IU/mL.