HBsAg quantification to optimize treatment monitoring in chronic hepatitis B patients.

Hepatitis B surface antigen (HBsAg) levels in serum have been shown to reflect active intrahepatic covalently closed circular DNA (cccDNA) and to have additional value as a marker of on-treatment efficacy. In the past few years, immunoassays to quantify HBsAg have been developed to monitor HBsAg kinetics during treatment. Although HBsAg quantification cannot replace HBV DNA measurement in clinical practice, the combined use of HBsAg quantification and HBV DNA measurements could help predict treatment outcome. One of the most important results of the studies in this new marker is that a decline in HBsAg titres during pegylated-interferon (PEG-IFN) treatment is a strong predictor of response so that a 'week 12 stopping rule' could be established for both Hepatitis B e antigen (HBeAg)-positive and HBeAg-negative patients. However, the positive predictive value (PPV) for a sustained viral response (SVR) remains low. The role of HBsAg measurements during nucloes(t)ides analogue (NAs) treatment is unclear. It may be a useful marker for stopping NAs by limiting the chance of relapse or for add-on strategies. Monitoring serum HBsAg levels in chronic hepatitis B (CHB) patients during treatment may provide significant complementary information to HBV DNA measurements.