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Varicella Zoster Virus Antibody (IgG)

Test code(s) 4439

Question 1. Does a positive IgG result indicate immunity to varicella zoster virus (VZV)?

VZV IgG testing is useful for the determination of an individual’s immune status and/or to aid in the diagnosis of varicella zoster infection. A positive VZV IgG result indicates the presence of antibodies to varicella zoster virus. The test cannot distinguish between past infection and current infection though, so a positive result could indicate active infection and not immunity. If active infection is not suspected based on the patient’s history, clinical presentation, and other laboratory results, then a positive IgG result is likely due to past infection. In such a case, the patient is presumed to be immune to varicella zoster virus.    

Question 2. What does a negative VZV IgG result mean in a patient who has been vaccinated?

Vaccinated individuals generally have a lower level of VZV antibodies than do patients with a history of infection. This assay can readily detect antibodies from a past infection, but it might not be able to detect antibodies in all vaccinated people.

An undetectable level of antibody, however, does not necessarily mean the vaccinated person is susceptible to varicella infection. Given the potential for negative test results, post-vaccination serologic testing is not recommended.

Question 3. What does an equivocal result mean?

An equivocal VZV IgG result (index value of 0.91-1.09) indicates a borderline result. A new serum sample should be collected and tested 10-14 days after the original sample.

 
References
 
  1. Centers for Disease Control and Prevention (CDC). Varicella. In: Atkinson W, Wolfe S, Hamborsky J, eds. Epidemiology and Prevention of Vaccine-Preventable Diseases. 12th ed. Washington DC: Public Health Foundation; 2012. http://www.cdc.gov/vaccines/pubs/pinkbook/varicella.html. Accessed November 22, 2013.
  2. Chernecky CC, Berger BJ. Laboratory Tests and Diagnostics Procedures. 5th ed. St. Louis, MO: Saunders Elsevier; 2008:1156.  
This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
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