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. IgM antibodies are the first to be produced by the body in response to a VZV infection. They are present in most individuals within a week or two after the initial exposure. IgM antibody production rises for a short time period and declines. Eventually, the level (titer) of VZV IgM antibody usually falls below detectable levels. Additional IgM may be produced when latent VZV is reactivated. 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.