Testing for Hepatitis A and E
For acute hepatitis A, order HAV IgM antibody; for acute hepatitis E, order both HEV IgM antibody AND HEV RNA (nucleic acid amplification test/NAAT) together. 1, 2
Hepatitis A Testing
Primary Diagnostic Test
- HAV IgM antibody confirms acute hepatitis A infection 1
- Specimen: serum or plasma (EDTA or plasma preparation tube)
- Transport at room temperature within 2 hours 1
Important Caveat
False-positive HAV IgM results can occur in populations with low prevalence of acute hepatitis A due to poor positive predictive value of available assays 1. If clinical suspicion is low and the test is positive, consider this possibility.
Additional Markers
- HAV IgG antibody indicates past infection or vaccination immunity, not acute infection 1
- HAV total antibodies combined with normal liver tests and absence of IgM suggests resolved infection 1
Hepatitis E Testing
Dual Testing Approach Required
The key difference from hepatitis A is that hepatitis E requires BOTH serologic and molecular testing for reliable diagnosis. 2
Standard Testing Algorithm
- HEV IgM antibody (appears 4-6 weeks post-exposure, lasts 2-4 months) 1
- HEV RNA by NAAT (detects current infection) 1, 2
Why Both Tests Are Necessary
The 2018 EASL guidelines explicitly recommend using a combination of serology and NAT testing to diagnose HEV infection 2. Research confirms poor inter-test agreement between IgM and RT-PCR, with one study showing IgM detected only 23.9% while RT-PCR detected 32.6% of cases—combining both identified 50% of acute hepatitis cases 3. Anti-HEV IgM alone is not sufficiently robust for diagnosis 2.
Special Populations Requiring Molecular Testing
- Immunosuppressed patients (organ transplant recipients): Often have undetectable anti-HEV antibodies due to delayed humoral response, making HEV RNA the only reliable diagnostic method 1
- Chronic hepatitis E (≥3 months HEV viremia): Requires HEV RNA quantification for diagnosis and monitoring 1
Specimen Requirements
- Serum or plasma (EDTA or plasma preparation tube)
- Transport at room temperature within 2 hours 1
Clinical Context
When to Test
Since acute hepatitis A and E are clinically indistinguishable from each other 1, test for both simultaneously when evaluating acute hepatitis. The EASL guidelines state that all patients with hepatitis should be tested for HEV as part of first-line virological investigation, not as a second-line test after other viruses are excluded 2.
Timing Considerations
HEV RNA appears earlier than antibodies (around 3 weeks post-infection, before symptom onset), while IgM appears later (4-6 weeks) 2. One study found RT-PCR positive patients had significantly shorter illness duration (mean 8.6 days) compared to RT-PCR negative patients (11.66 days), suggesting RNA testing is more sensitive early in disease 3.
Common Pitfall
Do not rely on travel history to decide whether to test for hepatitis E. Most hepatitis E cases in developed countries are locally acquired (not travel-related), often from zoonotic transmission 2. Testing algorithms that only consider HEV in travelers are outdated and will miss the majority of cases.
Additional Diagnostic Option
HEV antigen detection by enzyme immunoassay can diagnose both acute and chronic infections, though newer assays are needed for optimal sensitivity 2. This is not yet standard first-line testing.