The diagnosis of an active infection by the hepatitis B virus (HBV) relies on testing for the HBV surface antigen (HBsAg). Over the decades the sensitivity of HBsAg assays has increased, and the most recent solutions attain a level of 5 mIU/mL and enable to detect active HBV also at very low level of expression, with HBV-DNA levels <100 mIU/mL. The availability of such assays will help improve the safety of blood screening in settings that do not encompass testing for HBV-DNA and will enable unveiling HBsAg in a substantial share of "occult" or "latent" HBV infections (OBI). Unveiling OBIs has a great clinical relevance in immunocompromised or immunosuppressed patients and in people coinfected by other viruses, such as HCV or HIV. Additionally, since the negativity for HBsAg is a major endpoint for antiviral treatment with nucleosi(t)ide analogues, a higher sensitivity for HBsAg can help with a safer interruption of treatment.

 

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