Quantitative hepatitis B surface antigen (qHBsAg) and quantitative hepatitis B e antigen (qHBeAg) titers are emerging as useful tools for measuring viral loads and for predicting the virological response (VR) and serological response (SR) to pegylated interferon therapy. However, the clinical utility of these assays in patients taking entecavir (ETV) is largely unknown. Treatment-naive patients with chronic hepatitis B (CHB) who were taking ETV for 2 years were enrolled. The qHBsAg and qHBeAg levels were serially measured with the Architect assay. From 95 patients, 60.0% of whom were hepatitis B e antigen-positive [HBeAg(+)], 475 samples were analyzed. The median baseline log hepatitis B virus (HBV) DNA, log qHBsAg, and log qHBeAg values were 6.73 copies/mL (4.04-9.11 copies/mL), 3.58 IU/mL (1.17-5.10 IU/mL), and 1.71 Paul Ehrlich (PE) IU/mL (-0.64 to 2.63 PE IU/mL), respectively. For the prediction of VR (HBV DNA < 60 copies/mL at 24 months) in HBeAg(+) patients, baseline alanine aminotransferase (P = 0.013), HBV DNA (P = 0.040), and qHBsAg levels (P = 0.033) were significant. For the prediction of VR, the area under the curve for the baseline log qHBsAg level was 0.823 (P < 0.001); a cutoff level of 3.98 IU/mL (9550 IU/mL on a nonlogarithmic scale) yielded the highest predictive value with a sensitivity of 86.8% and a specificity of 78.9%. As for SR (HBeAg loss at 24 months), the reduction of qHBeAg was significantly greater in the SR(+) group versus the SR(-) group. The sensitivity and specificity were 75.0% and 89.8%, respectively, with a decline of 1.00 PE IU/mL at 6 months. With ETV therapy, the correlation between HBV DNA and qHBsAg peaked at 6 months in HBeAg(+) patients.

Conclusion: Both qHBsAg and qHBeAg decreased significantly with ETV therapy. The baseline qHBsAg levels and the on-treatment decline of qHBeAg in HBeAg(+) patients were proven to be highly useful in predicting VR and SR, respectively. The determination of qHBsAg and qHBeAg can help us to select the appropriate strategy for the management of patients with CHB. However, the dynamic interplay between qHBsAg, qHBeAg, and HBV DNA during antiviral therapy remains to be elucidated.