EBV Ab/VCA IgG Test
The EBV Ab/VCA IgG test is a serological test that detects immunoglobulin G antibodies against the viral capsid antigen of Epstein-Barr virus, primarily used to determine past exposure to EBV infection. 1
What This Test Measures
The EBV Ab/VCA IgG test specifically measures antibodies that target the viral capsid antigen (VCA) of Epstein-Barr virus. This test is part of a comprehensive EBV serological panel that helps differentiate between:
- Recent primary infection
- Past infection
- Reactivation of latent infection
Clinical Significance
Interpretation of Results
Positive VCA IgG: Indicates current or past EBV infection
- Over 90% of the normal adult population has IgG class antibodies to VCA antigens 1
- VCA IgG antibodies develop during acute infection and persist for life
- The presence of VCA IgG alone (without VCA IgM and with EBNA antibodies) typically indicates past infection
Negative VCA IgG: Suggests no prior exposure to EBV
Diagnostic Algorithm for EBV Infection Status
To properly interpret EBV Ab/VCA IgG results, they should be evaluated alongside other EBV markers:
Recent primary infection pattern:
- Positive VCA IgM
- Positive VCA IgG (often with low avidity)
- Negative EBNA antibodies 1
Past infection pattern:
- Negative VCA IgM
- Positive VCA IgG (high avidity)
- Positive EBNA antibodies 1
Late primary infection or reactivation pattern:
- Positive VCA IgM
- Positive VCA IgG
- Positive EBNA antibodies
- In this case, IgG avidity testing is crucial to differentiate between late primary infection (low avidity) and reactivation (high avidity) 2
Clinical Applications
The EBV Ab/VCA IgG test is particularly useful in:
- Diagnosing infectious mononucleosis when heterophile antibody tests (Monospot) are negative (occurs in approximately 10% of patients, especially children under 10 years) 1
- Differentiating EBV infection from other causes of mononucleosis-like illness (CMV, adenovirus, HIV, Toxoplasma gondii)
- Determining immune status to EBV
- Evaluating patients with suspected EBV-associated lymphoproliferative disorders
Important Considerations and Pitfalls
- Timing matters: VCA IgG antibodies typically develop within 1-2 weeks after symptom onset and persist for life 1
- Avidity testing: When both VCA IgG and IgM are present, avidity testing of VCA IgG can help distinguish between recent primary infection (low avidity) and past infection/reactivation (high avidity) 2
- False positives: Cross-reactivity with other herpesvirus infections can occur
- Interpretation challenges: The combination of positive VCA IgG, positive VCA IgM, and positive EBNA-1 antibodies can occur in both late primary infection and during subclinical viral reactivation 3
- Test limitations: Approximately 5-10% of patients who have been infected with EBV fail to develop antibodies to the EBNA antigen, which can complicate interpretation 1
Specimen Collection and Handling
- Specimen type: Serum (clot tube)
- Transport conditions: Room temperature
- Optimal transport time: Less than 2 hours 1
The EBV Ab/VCA IgG test is an essential component of EBV serological testing and, when interpreted correctly alongside other EBV markers, provides valuable diagnostic information about a patient's EBV infection status.