Varicella Zoster virus (VZV) is a herpes virus causing Chickenpox as a primary infection & Herpes zoster due to reactivation of latent infection. A positive IgG result indicates exposure to VZV and immunity. IgM antibodies are useful for diagnosing acute phase infection with VZV. Negative results in suspected early VZV infection should be followed by serial testing 2-3 weeks apart.