The positive duration of varicella zoster immunoglobulin M antibody test in herpes zoster.

Laboratory tests for herpes zoster (HZ) are required to confirm varicella zoster virus (VZV) infection, especially when a skin lesion is not typical or apparent. The serological test for VZV IgM antibody is simple and cost-effective; however, the change in the VZV IgM-positive rate over the time course of the disease has not been investigated. Therefore, we conducted an observational study to evaluate the positive rate of VZV IgM results during the time course of HZ and estimate the VZV IgM-positive period.After obtaining serum from patients with typical HZ, the VZV IgM titer was examined using enzyme-linked immunosorbent assay methods. After logarithmic transformation of the VZV IgM titer and the period after the onset of HZ, regression analysis was performed with the 2 transformed variables.A total of 62 patients were included in this study, and VZV IgM antibody was positive only in 23 patients (37%). The estimated antibody-positive period after HZ onset was 3.5 weeks (95% confidence interval 2.8-4.6 weeks).These findings suggest that the serological diagnosis of VZV IgM to confirm HZ is only useful within 3.5 weeks after the onset of symptoms.