antiHBs

Anti-HBs, or hepatitis B surface antibody (HBsAb), are antibodies directed against the hepatitis B virus surface antigen (HBsAg). They are produced by the immune system in response to vaccination with a recombinant hepatitis B vaccine or after recovery from natural infection. The presence of anti-HBs in the blood generally indicates immunity to hepatitis B and a reduced risk of chronic infection if exposed to the virus. Anti-HBs antibodies help neutralize HBV and prevent viral entry into liver cells.

Serology and interpretation: A positive anti-HBs test with negative HBsAg and negative anti-HBc typically indicates immunity from vaccination. If anti-HBs is positive in the presence of anti-HBc (and HBsAg negative), this usually reflects immunity from past natural infection. If anti-HBs is negative, HBsAg is negative, and anti-HBc is positive, this may indicate resolved infection with waning anti-HBs, or a window period during acute infection when anti-HBs has not yet appeared. In the acute phase of infection, HBsAg is positive and anti-HBs is negative, with anti-HBc IgM often present during the early period.

Protective levels and duration: A concentration of anti-HBs of at least 10 mIU/mL is commonly used as a protective threshold after vaccination. Antibody levels can wane over time, but immune memory can persist, supporting long-term protection. Booster vaccination is not routinely recommended for immunocompetent individuals, though some groups (such as certain patients with immune suppression or ongoing exposure risk) may require assessment and booster schedules per guidelines.

Limitations: Anti-HBs does not indicate current infection if HBsAg is present; a person can be infected and yet have detectable anti-HBs in some scenarios. Serologic interpretation should consider the full HBV profile, including HBsAg and anti-HBc.