Analysis of Borderline and Low Level Reactive Hepatitis B Virus Surface Antigen (HBsAg) by Different Automated HBsAg Assay

Abstract

Hepatitis B virus (HBV) surface antigen (HBsAg) has been used as the first-line marker to detect HBV infection. However, HBsAg assay could give false positive result. The objective of this study was to define the signal cutoff in borderline and low level reactive HBsAg results in order to interpret positive HBsAg results correctly. The retrospective study of data collected from automated HBsAg assays at Clinical Immunology Unit, Department of Pathology, Ramathibodi Hospital from January 2011 to May 2017 was conducted. The total 651 HBSAg test results that Architect HBsAg assay showed signal-to-cutoff (s/co) ratios 0.9 to 20 were included in this study. The interpretation of HBsAg results was confirmed by second automated HBsAg assays, either Elecsys HBsAg II, Vitros HBsAg or Vidas HBsAg. In addition, the test results of HBsAg assay were compared with HBV viral load.

The second HBsAg assays confirmed 59% positive HBsAg, 18% intermediate HBsAg, and 23% negative HBsAg. When Architect HBsAg showed signal ≥10 s/co ratios, the second assays confirmed 98% positive HBsAg and 2% intermediate HBsAg without negative HBsAg. The Architect HBsAg assay correlated with the second assays; Elecsys HBsAg II, Vitros HBsAg and Vidas HBsAg, (r = 075, 0.65, and 0.60 respectively). However, only 47% of total samples were positive for HBV viral load.

In conclusion, borderline and low level reactive Architect HBsAg results that showed signal <5 s/co ratios needed confirmation by the second assays before HBsAg interpretation and report. Architect HBsAg test results that showed signal ≥10 s/co ratios could be precisely predicted positive HBsAg results.