Implications of a Positive Varicella Antibody IgG Test Result
A positive Varicella-Zoster Virus (VZV) IgG antibody test indicates immunity to chickenpox, either from previous natural infection or vaccination, and generally means the person is protected against future VZV infection. 1 This immunity is typically long-lasting and provides protection against both primary varicella infection (chickenpox) and reduces the risk of herpes zoster (shingles).
Clinical Significance of Positive VZV IgG
- Confirms immunity status: A positive VZV IgG test is considered evidence of immunity to varicella 2
- No need for vaccination: Individuals with positive VZV IgG do not require varicella vaccination 2
- Reduced risk of infection: Immune individuals are protected against primary varicella infection and have reduced risk of developing herpes zoster 1
- Occupational clearance: Healthcare workers with positive VZV IgG can work with high-risk patients without restrictions related to varicella exposure 2
Special Populations Considerations
Immunocompromised Patients
- Despite positive VZV IgG, immunocompromised patients may have reduced VZV-specific lymphocytes and lower antibody avidity 1
- Bone marrow transplant recipients should be considered non-immune regardless of previous history of varicella or vaccination status 2
- In severely immunocompromised patients, a positive IgG may not always confer complete protection after exposure 3
Healthcare Workers
- A positive VZV IgG test in healthcare workers indicates they can safely work with patients without risk of transmitting or acquiring varicella 2
- Healthcare institutions should establish protocols for screening and managing healthcare personnel after exposures in the workplace 2
Testing Methods and Interpretation
The most widely used tests to detect varicella IgG antibodies are:
- Enzyme-linked immunosorbent assay (ELISA)
- Latex agglutination (LA) test 2
The LA test is generally more sensitive than commercial ELISAs but may produce false-positive results, particularly when only a single concentration of serum is evaluated 2
For screening healthcare personnel for varicella susceptibility, a less sensitive but more specific commercial ELISA should be considered 2
Commercial assays may lack sensitivity in detecting vaccine-induced immunity and might give false-negative results in vaccinated individuals 2, 4
Limitations and Caveats
A positive VZV IgG test does not differentiate between immunity acquired through natural infection versus vaccination 1
Commercial VZV ELISA assays were designed to measure higher titers associated with natural infection rather than the lower titers induced by the vaccine 4
In some individuals, the antibody response to VZV vaccine may be low despite an adequate cell-mediated immune response 4
Antibody levels may wane over time, but this doesn't necessarily indicate loss of protection due to persistent cell-mediated immunity 5
Post-Exposure Management
Individuals with positive VZV IgG do not require post-exposure prophylaxis with Varicella Zoster Immune Globulin (VariZIG) when exposed to varicella 2, 1
Healthcare workers with documented immunity (positive VZV IgG) who are exposed to VZV do not need to be furloughed or receive post-exposure vaccination 2
For immunocompromised patients with positive VZV IgG who are exposed to varicella, clinical judgment should be used regarding the need for prophylaxis based on the degree of immunosuppression 2, 3
In summary, a positive Varicella antibody IgG test generally indicates protective immunity against varicella infection, though certain populations (particularly immunocompromised patients) may require special consideration despite positive antibody status.