TzanckTest

The Tzanck test, also known as the Tzanck smear, is a rapid cytologic technique used in dermatology to identify cellular changes associated with certain vesiculobullous diseases. It is most often applied to vesicular or ulcerative lesions to help distinguish herpesvirus infections and pemphigus vulgaris. A positive result supports a clinical impression of herpes simplex virus (HSV) or varicella-zoster virus (VZV) infection, or pemphigus vulgaris, depending on the cytologic findings.

Procedure and interpretation: Cells are collected from the base of a vesicle or ulcer by gently scraping with a glass slide. The specimen is smeared on a slide, fixed, and stained with a supravital or Romanowsky-type stain (for example, Wright or Giemsa). Under light microscopy, the presence of multinucleated giant cells suggests herpesvirus infection, while acantholytic keratinocytes supports pemphigus vulgaris. The test does not distinguish HSV from VZV and cannot reliably identify all herpesviruses or other causes of vesicles.

Limitations and use: The Tzanck test is a rapid, inexpensive bedside tool but has limited sensitivity and specificity and requires experienced interpretation. A negative result does not exclude disease. In contemporary practice, more specific methods such as PCR, direct immunofluorescence, or viral culture are preferred for definitive diagnosis. The test is less commonly used in high-resource settings but can remain valuable in resource-limited environments or for teaching purposes.

History: The test is named after Arnoldo Tzanck, who described the technique in the mid-20th century.