A method for determining the cut-off value of a varicella-zoster virus IgG enzyme immunoassay for immune status

The cut-off optical density (OD) of an enzyme immunoassay (EIA) for IgG antibody to varicella-zoster virus (VZV) was established by application of a statistical technique to OD readings on sera from known susceptible and immune populations. Children aged one to three years who lacked complement fixation (CF) antibody were considered to be known susceptible subjects. Adults whose sera contained antibody by the CF test were considered to be known immune subjects. The method provides a valid alternative to previously used techniques of establishing a cut-off OD, above which reading the EIA can be taken to indicate immunity to varicella-zoster infection.