Diagnostic Testing for Hepatitis E Virus
Use a combination of HEV serology (anti-HEV IgM and IgG) plus HEV RNA nucleic acid testing (NAT) to diagnose hepatitis E virus infection, with NAT being essential for immunosuppressed patients who may not mount an antibody response. 1
Primary Diagnostic Tests
1. Nucleic Acid Testing (NAT) for HEV RNA
HEV RNA detection in blood or stool is the definitive indicator of active HEV infection 1. This is the gold standard, particularly critical in specific populations:
- Real-time RT-PCR is the most commonly used method, targeting conserved regions of ORF2/ORF3 overlap 1
- Analytical sensitivity can reach <10 IU/ml 1
- Detects all four major genotypes (HEV-1 through HEV-4) that infect humans 1
- Mandatory in immunosuppressed patients where antibodies are often undetectable 1
Critical caveat: In immunosuppressed patients, up to 16.4% with active HEV infection have neither IgG nor IgM antibodies, making NAT the only reliable diagnostic method 2. Missing this can lead to chronic infection.
2. Serological Testing (Antibodies)
Anti-HEV IgM and IgG enzyme immunoassays are used for acute infection diagnosis, but never rely on IgM alone due to suboptimal specificity 1:
- IgM antibodies: Appear at symptom onset, persist 3-4 months (occasionally up to 1 year) 1
- IgG antibodies: Appear shortly after IgM, provide long-lasting immunity 1
- Diagnostic approach: Detection of anti-HEV IgM plus rising IgG titers confirms acute infection 1
Important limitation: Serological testing alone is insufficient—always combine with NAT for definitive diagnosis 1. Isolated IgM positivity should be confirmed with additional testing 3.
3. HEV Antigen Testing
HEV antigen detection by enzyme immunoassay can diagnose both acute and chronic infections 1:
- Newer assays show improved sensitivity approaching NAT 1
- Particularly useful in outbreak settings where RNA testing is unavailable 4
- Limitation: HEV antigen may persist months after RNA clearance following ribavirin treatment, so does not necessarily indicate infectious virions 1
Diagnostic Algorithm by Clinical Scenario
For Immunocompetent Patients:
- Screen with anti-HEV IgM and IgG simultaneously
- If either positive or clinical suspicion remains high, perform HEV RNA testing 2
For Immunosuppressed Patients (transplant recipients, HIV, chemotherapy):
- Always perform HEV RNA testing directly—do not rely on serology alone 1, 2
- Antibodies are frequently absent despite active infection
- Chronic HEV is defined as HEV RNA detectable for ≥3 months 1
When to Test:
- All patients with unexplained hepatitis, regardless of travel history 1
- Test HEV as first-line alongside HAV, HBV, HCV—not as a second-line test 1
- Suspected drug-induced liver injury (DILI): Always test for HEV, as 13% of presumed DILI cases are actually acute hepatitis E 1
Timeline of Test Positivity
Understanding when tests become positive guides interpretation 1:
- HEV RNA: Detectable ~3 weeks post-infection, before symptom onset; persists 3-6 weeks in blood, 4-6 weeks in stool
- IgM antibodies: Appear at symptom onset
- IgG antibodies: Appear shortly after IgM
- Biochemical markers: Elevated at clinical onset
Additional Diagnostic Tools
Immunohistochemistry for HEV ORF2 protein on liver biopsy can establish histopathologic diagnosis when needed 1.
Common Pitfalls to Avoid
- Never diagnose based on IgM alone—specificity is suboptimal; always confirm with NAT or rising IgG titers 1
- Never skip NAT in immunosuppressed patients—they frequently lack antibody response despite active infection 1, 2
- Don't wait for negative HAV/HBV/HCV results before testing HEV—test simultaneously as first-line 1
- Don't assume travel history is required—most HEV cases in developed countries are locally acquired 1
- Beware of false negatives from genetic polymorphisms in NAT assays—use assays targeting conserved regions 1