If the diagnosis is in doubt, laboratory confirmation can be done; it requires one of the following: Polymerase chain reaction (PCR) for viral DNA Immunofluorescent detection of viral antigen in lesions Serologic tests Viral culture Tzanck smear In serologic tests, detection of IgM antibodies to varicella-zoster virus (VZV) or seroconversion from negative to positive for antibodies to VZV indicate acute infection.