When someone is exposed to VZV, the person's immune system responds by producing antibodies to the virus. Laboratory tests can detect and measure the level of two classes of VZV antibodies in the blood: IgM and IgG. IgG antibodies are produced by the body several weeks after the initial VZV infection and provide long-term protection. Levels of IgG rise during the active infection, then stabilize as the VZV infection resolves and the virus becomes inactive. Once a person has been exposed to VZV, that person will have some measurable amount of VZV IgG antibody in their blood for the rest of their life. VZV IgG antibody testing can be used, along with IgM testing, to help confirm the presence of a recent or previous VZV infection.