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Tzanck preparation
Derm Principles > Section I. General Principles > 4. Diagnostic procedures > Tzanck preparation
Tzanck preparation (Tzanck smear) is a quick laboratory test to diagnose herpesvirus skin infections. It is AKA herpes stain for inclusion bodies and inclusion bodies stain. It is used to rapidly diagnose herpes simplex and varicella zoster infections.
- A Tzanck preparation is used to confirm a clinical impression of a herpes virus infection (classically grouped vesicles on an erythematous base). Especially in immunocompromised patients, moist ulcerations may form.
- The test is done by smearing cells taken from an intact vesicle or ulcer onto a microscope slide. It is rarely useful on a resolving, crusted lesion. A vesicle is unroofed with a scalpel or sterile needle, the base is scraped with the scalpel, and the material spread thinly on a slide. The smear is stained with Wright's stain (or similar), and examined microscopically. A diagnosis is often possible in minutes.
- Diagnostic changes are multinucelated giant cells with nuclei that appear molded together. The cell cytoplasm resembles "ground glass" and contains inclusion bodies.
- False negatives are fairly common (21-50%). While a positive Tzanck smear is diagnostic, a negative one may need confirmation by a herpes culture to avoid false negatives in clinically suspicious cases.
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