From the Guidelines
Hepatitis A antibody testing for immunity should focus on IgG antibodies, as they indicate long-term protection against the virus, rather than IgM antibodies which signify current or recent infection. The presence of IgG antibodies, whether from past infection or successful vaccination, confers long-term immunity to hepatitis A virus (HAV) 1. IgM antibodies, on the other hand, are indicative of a current or recent HAV infection, typically appearing 5-10 days before the onset of symptoms and persisting for less than 6 months 1.
To determine immunity, testing for total antibodies or specifically IgG antibodies is necessary. The distinction between IgM and IgG is crucial because IgM is the acute phase antibody that appears early in infection but diminishes over time, while IgG represents the long-term protective antibody that develops later and persists 1. For individuals seeking to confirm their immunity status before travel to endemic areas or after potential exposure, the appropriate test would be hepatitis A total antibodies or IgG, not IgM.
Key points to consider:
- IgG antibodies indicate long-term immunity to HAV.
- IgM antibodies signify current or recent infection.
- Testing for total antibodies or IgG is necessary to determine immunity.
- The choice between testing for IgM or IgG depends on whether the goal is to diagnose an active infection or to assess immunity. Understanding this difference helps healthcare providers select the correct test when evaluating a patient's immune status versus diagnosing active infection 1.
From the Research
Hepatitis A Antibody and Immunity
- The presence of hepatitis A antibodies, specifically IgG anti-HAV, indicates immunity from further infections of hepatitis A 2.
- Studies have shown that inactivated hepatitis A vaccines can induce long-term antibody persistence, with estimated persistence of antibodies within protective range varying between 24 and 47 years depending on individual titres reached at month 13 and vaccination dose 3.
- A single dose of inactivated hepatitis A vaccine may be a convenient alternative to immunoglobulin for inducing rapid seroprotection, with a booster dose at month 6 ensuring long-lasting protection 4.
- Delaying the booster dose up to 66 months after primary vaccination did not seem to influence the immunogenicity of the booster dose, although the recommended 6-12-month interval remains if detectable antibody titers are to be warranted constantly 5.
- Active vaccination with a single dose of inactivated hepatitis A vaccine may eventually replace immunoglobulin for pre-exposure prophylaxis, with postbooster anti-HAV titres rising to 73-fold greater than the peak GMT seen one week after immunoglobulin 6.
EGM and Immunity
- There is no direct evidence in the provided studies to suggest that hepatitis A antibody EGM determines immunity.
- However, the studies suggest that the presence of hepatitis A antibodies, specifically IgG anti-HAV, is indicative of immunity from further infections of hepatitis A 2.