The role of HBsAg levels in the current management of chronic HBV infection.

Chronic hepatitis B virus (HBV) infection can result in liver cirrhosis, hepatic decompensation, and hepatocellular carcinoma (HCC). However, the natural course of the disease is highly dynamic and not every patient requires therapy. The challenges for optimal management are who to treat, which therapeutic regimen to use, and when to begin or stop treatment. Constant monitoring is mandatory to predict the natural course and guide treatment decisions. Surrogate markers for baseline and on treatment decisions are needed. Besides HBV DNA, hepatitis B surface antigen levels also proved to be useful to help judge the natural course and guide treatment. High levels of HBsAg are suggestive of low fibrosis and immune tolerance in hepatitis B e antigen (HBeAg) positive patients; whereas low levels of HBsAg indicate a lower risk for HCC and inactive carrier state in HBeAg negative patients. Data also support the possible use of HBsAg levels as an on-treatment response marker. So far, the best evidence exists for treatment with interferon (IFN)-α where lack of HBsAg decline after 12 weeks is associated with non-response. Thus, stopping rules after 12 weeks therapy could be established for HBeAg positive as well as for HBeAg negative patients. However, the positive predictive value for achieving sustained response is still vague. The value of HBsAg monitoring is less clear during treatment with nucleos(t)ide analogues (NA) but it can be a useful marker for new concepts such as stopping NA or add-on IFN strategies. Currently, several studies are underway to validate HBsAg in these settings.