What is the role of lab testing in the diagnosis of varicella-zoster virus (VZV) infection?

Updated: Feb 15, 2019
  • Author: Wayne E Anderson, DO, FAHS, FAAN; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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When the presentation includes the typical dermatomal rash, additional studies are not required.

If the diagnosis is in doubt, a Tzanck smear can be performed and has a sensitivity of about 60%. To obtain a Tzanck smear, remove the crust from a vesicle and scrape the underlying moist skin with a No. 15 surgical blade. Smear the cells from the vesicle base onto a slide, fix for 1 minute with absolute alcohol, and stain with Wright stain (other staining methods can also be used).

The diagnosis can also be confirmed with a culture of vesicular fluid that is positive for varicella-zoster virus (VZV).

In cases of zoster sine herpete, DNA analysis via polymerase chain reaction (PCR) can be used for early diagnosis if laboratory turnaround time is reasonably short. If not, the decision of whether to start empiric acyclovir must be based on clinical grounds alone.

In cases of acyclovir-resistant VZV, detections of mutations in thymidine kinase can be determined by PCR and sequence analysis. Acyclovir-resistance may occur in stem cell transplant recipients. [5]

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