Testing for Hepatitis A Immunity
Order a total anti-HAV (hepatitis A antibody) test to determine if a patient is immune to hepatitis A. This single test detects both IgM and IgG antibodies and is the recommended screening test for immunity 1.
Understanding the Test
Total anti-HAV is the appropriate test for assessing immunity because:
- A positive total anti-HAV result indicates immunity from either past infection or vaccination 2, 3
- This antibody persists for life and provides lifelong protection against reinfection 1, 2
- The test is specifically used by clinicians to determine whether a person with an indication for pre-exposure prophylaxis is already immune 1
Interpreting Results
If Total Anti-HAV is Positive (Reactive)
- The patient is immune - no further hepatitis A vaccination is needed 2, 3, 4
- Immunity is lifelong whether from natural infection or vaccination 1, 2
- No follow-up testing is necessary 4
If Total Anti-HAV is Negative
- The patient is susceptible and should receive hepatitis A vaccination 1
- Prevaccination screening is cost-effective when seroprevalence exceeds 30% in the patient population 1
When Additional Testing May Be Needed
If you need to distinguish acute infection from past immunity (e.g., patient presents with acute hepatitis symptoms):
- Order IgM anti-HAV in addition to total anti-HAV 1
- IgM positive indicates acute or recent infection (typically within past 6 months) 1, 2, 3
- IgM negative with total anti-HAV positive indicates past infection or vaccination immunity 2, 3
- IgM becomes detectable 5-10 days before symptom onset 1
Important Clinical Caveats
Be aware of potential false-positive IgM results:
- IgM anti-HAV can remain positive for >1 year after infection in some patients 1
- False-positive IgM tests can occur in persons without recent HAV infection, particularly due to polyclonal immune stimulation 1, 5, 6
- In elderly patients with positive IgM, consider immune reactivation rather than acute infection - an IgG avidity test (if available) showing high avidity (>70%) suggests past infection rather than acute disease 5, 6
- Most positive IgM results in current practice represent resolved or indeterminate infections rather than acute hepatitis A, given successful vaccination programs 7
Assay sensitivity differences matter:
- Some early acute hepatitis A patients may show anti-HAV IgM non-reactive but total anti-HAV reactive results due to higher IgM detection sensitivity of the total assay 8
- If clinical suspicion for acute hepatitis A is high despite negative IgM, repeat testing in 2-3 days or use total anti-HAV 8
Special Populations
- HIV-infected patients: Screen with total anti-HAV upon initiation of care; those at risk should be screened annually 1
- Chronic liver disease patients: Having positive anti-HAV is beneficial as it protects against additional liver damage from acute hepatitis A 2, 4
- Immunocompromised individuals: Antibody protection may wane more quickly; discuss results with their healthcare provider 2, 4