Chicken pox is caused by the varicella zoster virus (VZV). This test determines a person’s immune status against the varicella zoster virus. When the body is infected with VZV, it defends itself by producing two types of antibodies in sequence: first, IgM, which appears 1 to 2 weeks after the infection and which is present for a few weeks before disappearing, then IgG, which appears a few weeks after IgM and which lasts for the rest of that person’s life. IgG provides long-term immunity (protection), whether due to a prior infection by the virus or due to vaccination. However, the virus remains latent in the body and tends to reactivate with reduced immunity in adults over age 50, causing shingles. Testing for anti-VZV IgG and/or IgM is therefore used to diagnose the presence of the disease or the status of immunity against this infection.
The anti-chicken-pox-shingles IgG and IgM combination is sometimes used to detect a current or very recent infection. Negative IgG results combined with positive IgM results allow for a rapid diagnosis of infection, but it must be confirmed by the appearance (or significant increase) of IgG levels one to three weeks later. A low (inconclusive) positive result may occur during seroconversion (replacement of IgM with IgG) or may indicate old immunity (previous infection).