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Diagnostic Tests – Tzanck Smear

1. What is this?

A Tzanck smear is a cytologic test used to evaluate vesicular skin or mucosal lesions. Cells are scraped from the base of a vesicle, stained, and examined under a microscope. The key finding is the presence of multinucleated giant cells, which are characteristic of herpetic infections.

Importantly, the Tzanck smear cannot distinguish between:
  • Herpes simplex virus (HSV)
  • Varicella-zoster virus (VZV)
2. When is this the answer?
You should answer Tzanck smear as the best initial diagnostic test when:
  • A patient presents with vesicular skin or genital lesions
  • A herpetic infection (HSV or VZV) is suspected
  • The diagnosis is not clinically obvious
Exam pearl:
Vesicles + possible herpes → Tzanck smear first

If the classic clustered vesicles on an erythematous base are clearly present, testing may not be necessary.

3. What is the most accurate diagnostic test?

The most accurate diagnostic test for herpetic skin or genital infections is a:
  • Viral culture
(Modern practice may also use PCR, but for exam purposes, viral culture is the expected answer.)

High-yield Summary
  • Tzanck smear → quick, bedside, shows multinucleated giant cells
  • Cannot differentiate HSV vs VZV
  • Gold standard → viral culture


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Kembara Xtra 

Facts about medicine and its subtopic such as anatomy, physiology, biochemistry, pharmacology, medicine, pediatrics, psychiatry, obstetrics and gynecology and surgery.