Hepatitis D (HDV) Test
Hepatitis D (HDV) Testing: Complete Guide to IgM, Total Antibody, and HDV RNA
🦠 What Is Hepatitis D (HDV)?
Hepatitis D is a viral hepatitis caused by the Hepatitis D Virus (HDV), a defective RNA virus with a unique dependence on the Hepatitis B Virus (HBV).
Key Features
- HDV cannot replicate on its own
- Infection is possible only when HBV (HBsAg) is present
- Found exclusively in HBsAg-positive individuals
- Can occur as:
- Coinfection — HDV + HBV acquired at the same time
- Superinfection — HDV infection in someone with chronic HBV (much more severe)
Superinfection often leads to severe hepatitis, rapid fibrosis progression, or liver failure, making HDV one of the most clinically significant hepatitis viruses worldwide.
🧪 Types of HDV Tests
HDV testing includes serologic assays and molecular assays.
1) Anti-HDV IgM
- Indicates recent or acute HDV infection
- Strongly positive in superinfection
- Useful for identifying HDV-related acute hepatitis
2) Anti-HDV Total (IgG ± IgM)
- Marker of past or chronic HDV infection
- Used for screening HBsAg-positive patients
- Remains positive for years
3) HDV RNA (PCR)
- Confirms active viral replication
- Guides treatment decisions
- Essential for distinguishing past vs. active infection
➡️ Most clinical guidelines recommend Anti-HDV Total as the primary screening test for all HBsAg-positive patients.
🎯 Clinical Purpose of Each Test
| Test | Clinical Use |
|---|---|
| Anti-HDV IgM | Acute infection, superinfection identification |
| Anti-HDV Total | Past infection or chronic HDV evaluation |
| HDV RNA | Confirms active infection; used for treatment decision |
🔬 Test Method — Immunoassay (EIA / CLIA / CMIA)
HDV serology is performed using automated immunoassay platforms.
Principle of Immunoassay
- HDV antigens bind to patient antibodies (IgM or IgG)
- Signal detected via enzyme reaction, fluorescence, or chemiluminescence
- Reported as reactive / non-reactive or index values
Specimen
- Serum or plasma
- Fasting not required
📊 Reference Ranges (Typical Values)
(Ranges vary by manufacturer)
Anti-HDV IgM
- Negative → No acute infection
- Positive → Acute HDV infection or superinfection likely
Anti-HDV Total
- Negative → No evidence of past HDV
- Positive → Past or current HDV exposure (requires HDV RNA for clarification)
🧬 HDV: Clinical Significance
1) HBV + HDV Coinfection (simultaneous infection)
- Often presents with acute severe hepatitis
- IgM strongly positive
- Typically does NOT progress to chronic HDV
- ALT markedly elevated
2) HDV Superinfection (HDV added to chronic HBV)
- Much more severe clinical course
- Rapid progression to cirrhosis or liver failure
- Higher ALT/AST levels
- Anti-HDV IgM and IgG both strongly positive
- Higher likelihood of chronic HDV infection
➡️ Superinfection is clinically the most dangerous form of HDV infection.
📉 Serology Interpretation Summary
| Serologic Pattern | Interpretation |
|---|---|
| IgM (+) | Acute HDV infection or superinfection |
| IgM (-), Total (+) | Past exposure or chronic HDV → Check HDV RNA |
| IgM (-), Total (-) | No evidence of HDV infection |
Superinfection is strongly suspected when:
- HBsAg positive
- ALT markedly elevated
- Anti-HDV IgM (+) and/or HDV RNA (+)
⚠️ Important Considerations When Interpreting HDV Tests
1) HDV testing is only meaningful when HBsAg is positive
HDV cannot infect without HBV.
→ Always verify HBsAg(+) before interpreting HDV results.
2) IgM false positives
Possible in:
- Autoimmune diseases
- Nonspecific IgM elevation
- Cross-reactive antibodies
→ Use HDV RNA for confirmation.
3) Distinguishing coinfection vs superinfection
Use:
- ALT/AST trends
- IgM/IgG patterns
- HBV DNA level
- HDV RNA status
4) HDV RNA is the gold standard
Essential for:
- Diagnosis of active infection
- Monitoring response to therapy
- Guiding treatment decisions (e.g., interferon-based therapy)
🧾 Summary Table
| Item | Key Points |
|---|---|
| Testing Method | Immunoassay (EIA/CLIA/CMIA) |
| IgM | Acute infection / superinfection |
| Total Antibody | Past or chronic infection |
| HDV RNA | Confirms active infection |
| Specimen | Serum |
| Critical Note | HDV testing only meaningful if HBsAg(+) |
📚 References
- Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 6th ed.
- WHO Guidelines for Hepatitis D
- CDC Viral Hepatitis Surveillance
- EASL Clinical Practice Guidelines: Hepatitis Delta Virus Infection
- Henry’s Clinical Diagnosis and Management by Laboratory Methods, 24th ed.