What does a reactive anti‑hepatitis A virus IgG (anti‑HAV IgG) test indicate?

Interpretation of Reactive Anti-HAV IgG

A reactive anti-hepatitis A virus IgG (anti-HAV IgG) test indicates past exposure to hepatitis A virus—either from prior natural infection or from vaccination—and confirms immunity to hepatitis A. 1

What Anti-HAV IgG Positivity Means

• The presence of anti-HAV IgG antibody signifies either resolved past hepatitis A infection or immunity acquired through vaccination. 1
• Anti-HAV IgG antibodies appear 10–12 days after symptom onset during acute infection and remain detectable for months to years, providing long-lasting immunity. 1
• This result confirms the individual is protected against future hepatitis A infection and is not currently infectious to others. 1

Distinguishing Past Infection from Vaccination

• Standard anti-HAV IgG assays detect antibodies to the viral capsid proteins, which are produced both after natural infection and after vaccination with inactivated or attenuated HAV vaccines. 1
• These routine serologic tests cannot differentiate natural infection from vaccine-induced immunity, as both generate antibodies against structural proteins. 2
• If clinical distinction is required (e.g., for epidemiologic purposes), specialized testing for antibodies to non-structural HAV proteins (P2 or P3 region) can identify natural infection, since these proteins are only produced during active viral replication and not present in vaccines. 3, 2

Confirming Immunity Status

• The same immunity status (past infection or vaccination) can be confirmed by detecting total anti-HAV antibodies (combined IgG and IgM) in an asymptomatic patient with normal liver function tests and absence of anti-HAV IgM. 1
• The presence of anti-HAV IgG alone, without detectable IgM, rules out acute hepatitis A infection. 1

Clinical Pitfalls to Avoid

• Do not confuse anti-HAV IgG positivity with acute infection—acute hepatitis A is diagnosed by detecting anti-HAV IgM antibody, not IgG. 1
• Be aware that false-positive anti-HAV IgM results can occur in populations with low prevalence of acute hepatitis A due to low positive predictive value of assays. 1
• In rare early acute hepatitis A cases, anti-HAV IgM may be non-reactive while anti-HAV total (IgM and IgG combined) is reactive due to differences in assay sensitivity for detecting IgM antibodies. 4
• Anti-HAV IgG avidity testing (when available) can help distinguish recent acute infection (low avidity, <50%) from remote past infection or immune reactivation (high avidity, >70%), particularly in elderly patients where immune reactivation may cause false-positive IgM results. 5, 6

No Further Action Required

• Individuals with isolated anti-HAV IgG positivity (without IgM) require no treatment, no isolation precautions, and no further hepatitis A testing. 1
• They are immune and protected against reinfection with hepatitis A virus. 1