Interpretation of EBV IgG Result of 501
An EBV IgG value of 501 (units typically U/mL or arbitrary units depending on the laboratory) indicates past Epstein-Barr virus infection, as elevated IgG antibodies persist for life after primary infection and do not indicate acute or current disease. 1, 2
Understanding the Result
- IgG antibodies to EBV viral capsid antigen (VCA) develop during acute infection and remain elevated permanently, making them markers of past exposure rather than active disease 2, 3
- Over 90% of normal adults have detectable IgG antibodies to VCA from past infection, so this finding alone is expected in the general population 2
- The presence of VCA IgG without additional context (IgM status, EBNA status) cannot distinguish between recent and remote infection 4
Critical Next Steps for Complete Interpretation
To properly interpret this result and determine infection timing, you must evaluate:
- VCA IgM status: Positive IgM indicates acute or recent infection (within weeks to months), while negative IgM suggests remote infection 1, 2
- EBNA antibodies: The presence of EBNA antibodies indicates infection occurred more than 6 weeks prior, making EBV unlikely as the cause of current symptoms 1, 2
- Clinical context: Current symptoms suggestive of infectious mononucleosis versus asymptomatic screening 2
Diagnostic Algorithm Based on Additional Testing
If VCA IgG positive + VCA IgM positive + EBNA negative:
If VCA IgG positive + VCA IgM negative + EBNA positive:
- This indicates past infection (>2-3 months ago), and EBV is not the cause of current acute symptoms 1, 2
If VCA IgG positive + VCA IgM negative + EBNA negative:
- This pattern is ambiguous and requires IgG avidity testing to distinguish early acute infection from past infection with loss of EBNA response 4, 5
- Low avidity IgG suggests acute infection within 10-30 days 5
- High avidity IgG (>0.5) indicates past infection 5
When Elevated IgG Levels Suggest Active Disease
Markedly elevated VCA IgG titers (≥1:640) combined with elevated EA IgG (≥1:160) may indicate Chronic Active EBV Infection (CAEBV), particularly when accompanied by:
- Persistent infectious mononucleosis-like symptoms 6, 1
- Positive IgA antibodies to VCA and/or EA 6, 1
- EBV DNA levels >10^2.5 copies/mg DNA in peripheral blood mononuclear cells 1
Common Pitfalls to Avoid
- Do not interpret isolated VCA IgG results without VCA IgM and EBNA testing, as this provides incomplete information about infection timing 1, 2, 4
- Do not assume elevated IgG indicates active infection in immunocompetent patients—quantitative EBV viral load testing by nucleic acid amplification is required for suspected active disease in immunocompromised patients 1, 2
- Do not order repeat IgG testing for monitoring in immunocompetent patients, as IgG remains elevated for life and does not reflect disease activity 2
- In immunocompromised patients (transplant recipients, HIV-infected individuals), serology is unreliable and quantitative EBV DNA viral load testing should be used instead 1, 2