What blood work should be ordered to test for hepatitis A?

Testing for Hepatitis A

To test for hepatitis A, order IgM anti-HAV antibody testing on a serum or plasma sample as the primary diagnostic test for acute infection.

Diagnostic Testing Algorithm

Primary Test

• IgM anti-HAV antibody: The gold standard test for diagnosing acute hepatitis A infection 1
  • Specimen: Serum or plasma (collected in clot tube, SST, EDTA, or PPT)
  • Transport: Room temperature, within 2 hours 1

Interpretation of IgM anti-HAV Results

• Positive: Indicates acute or recent hepatitis A infection
  • IgM anti-HAV becomes detectable 5-10 days before symptom onset 1
  • Generally remains positive for up to 6 months after infection 1, 2
  • Note: Some patients may remain positive for longer periods (up to 420 days in rare cases) 2, 3
• Negative: No evidence of acute hepatitis A infection

Additional Testing (if clinically indicated)

• Total anti-HAV antibody (IgG and IgM): To determine immune status or past infection
  • Positive with negative IgM anti-HAV indicates past infection or immunity
  • Negative indicates susceptibility to hepatitis A

Clinical Considerations

When to Test for Hepatitis A

• Patients with symptoms of acute hepatitis (jaundice, elevated liver enzymes, fatigue)
• Individuals with known exposure to hepatitis A
• During outbreaks of hepatitis A
• Evaluation of abnormal liver function tests

Potential Pitfalls

1. False-positive IgM results: May occur in populations with low prevalence of acute hepatitis A 4

   • Consider clinical presentation when interpreting results
   • IgG avidity testing may help differentiate true acute infection from false positives 5

2. Prolonged IgM persistence: IgM anti-HAV can remain positive beyond the acute phase

   • Most patients become seronegative by 120 days after jaundice onset 2
   • Some patients (13.5%) may remain positive for >200 days 2

3. Testing too early: IgM anti-HAV may not be detectable in very early infection

   • If high clinical suspicion and negative result, consider repeat testing in 1-2 weeks

Documentation and Follow-up

• Document hepatitis A immunity status in the patient's medical record
• For patients with acute hepatitis A, monitor liver function tests until normalized
• Consider testing for other hepatitis viruses (B and C) if clinically indicated
• No specific follow-up testing for hepatitis A is needed after resolution unless new symptoms develop

By following this testing approach, you can accurately diagnose acute hepatitis A infection and distinguish it from past infection or immunity, allowing for appropriate clinical management and public health interventions.