Hepatitis B Surface Antigen and Antibody Interpretation

Introduction to Hepatitis B Surface Antigen (HBsAg)

The American Association for the Study of Liver Diseases recommends that HBsAg is a glycoprotein on the surface of the hepatitis B virus that serves as the hallmark of active HBV infection, appearing 1-10 weeks before symptom onset in acute infection 2
HBsAg positivity indicates current HBV infection (either acute or chronic) and confirms that the person is infectious, as stated by the Centers for Disease Control and Prevention 1, 2
Persistence of HBsAg beyond 6 months indicates progression to chronic HBV infection, according to the European Association for the Study of the Liver 3, 2
Quantification of HBsAg levels can be used for staging the natural history of HBV infection, evaluating response to therapy, as recommended by the American Gastroenterological Association 3
Low levels of both HBV DNA and HBsAg are associated with decreased risk of hepatocellular carcinoma (HCC), as reported by the National Comprehensive Cancer Network 3
During peginterferon alfa therapy, absence of decline in HBsAg by week 12 predicts non-response and may justify stopping therapy, as suggested by the American Association for the Study of Liver Diseases 3

The Centers for Disease Control and Prevention states that HBsAb indicates recovery from and immunity to HBV infection, resulting from either natural infection or vaccination 1
In most patients with self-limited acute HBV infection, HBsAg and HBsAb are not detectable simultaneously, as noted by the World Health Organization 1
Detection of HBsAb in the absence of HBc total antibodies distinguishes vaccine-derived immunity from immunity acquired by natural infection, according to the American Medical Association 1
Current commercially available assays for detecting HBsAb yield positive results when antibody levels are ≥10 mIU/mL, indicating protective immunity, as reported by the National Institute of Allergy and Infectious Diseases 1

The American Association for the Study of Liver Diseases recommends that HBsAg positive + Total anti-HBc positive + IgM anti-HBc positive = Acute HBV infection 2
HBsAg positive + Total anti-HBc positive + IgM anti-HBc negative = Chronic HBV infection, as stated by the European Association for the Study of the Liver 2
HBsAg negative + Total anti-HBc positive + Anti-HBs positive = Resolved HBV infection with natural immunity, according to the Centers for Disease Control and Prevention 4, 2
HBsAg negative + Anti-HBc negative + Anti-HBs positive = Immunity from vaccination, as recommended by the World Health Organization 2
HBsAg negative + Anti-HBc negative + Anti-HBs negative = Never infected, susceptible to infection, as noted by the American Medical Association 2

The European Association for the Study of the Liver states that occult HBV infection can occur when HBsAg is undetectable despite the presence of HBV DNA in serum or liver tissue 2
This is particularly important in immunocompromised patients with unexplained elevation of serum aminotransferase levels, as reported by the American Gastroenterological Association 3

The National Comprehensive Cancer Network reports that patients who are HBsAg negative but anti-HBc positive have a 3-45% risk of HBV reactivation when receiving immunosuppressive therapy 5, 4
The risk is particularly high with anti-CD20 monoclonal antibodies (e.g., rituximab), as noted by the American Society of Clinical Oncology 5, 4
Antiviral prophylaxis should be considered for HBsAg-positive or HBcAb-positive patients undergoing immunosuppressive therapy, as recommended by the Centers for Disease Control and Prevention 5

Transient HBsAg positivity can occur up to 18 days following vaccination (up to 52 days in hemodialysis patients), as stated by the American Association for the Study of Liver Diseases 2
False-negative HBsAg results may occur in chronic liver disease; viral load measurement should be considered in patients with a history of hepatitis, as reported by the National Institute of Allergy and Infectious Diseases 5