Method:
(1) An intact vesicle is identified.
(2) The skin surface is cleaned.
(3) The surface of the vesicle is punctured.
(4) The base of the vesicle is gently scraped with a scraper, paying attention to the edge of the blister base. The lesion should be firmly scraped with "enough" force, not too much and not too little.
(5) The fluid on the scraper is gently smeared on a slide.
(6) The slide is immediately fixed. The smear can be air-dried but morphology is better if the cells are fixed.
(7) The skin lesion is covered appropriately.
(8) The slide is stained. A Giemsa stain is widely used but almost any stain will do.
(9) The stained smear is examined for intranuclear inclusions (Cowdry type A) and/or multinucleated cells with nuclear molding.
Sensitivity is reduced if:
(1) the lesion is old, especially if crusted.
(2) too little force is used in scraping the skin lesion. A common mistake is only brush the scraper over the lesion.
(3) excessive force is used in making the smear
(4) the smear is hypocellular or shows only necrotic debris
(5) the person reading the smear is inexperienced
Sensitivity and/or specificity may be increased if:
(1) the test is combined with a viral detection method, especially PCR. A smear can be collected at the same time as the smear is taken.
(2) the smear is stained with an immune-based method such as immunofluorescence or Immunoperoxidase stain specific for the Herpes virus in question. Selection of the wrong stain can result in a false negative result.
Availability of real-time PCR makes the Tzanck smear obsolete at sites where PCR is available. However, it can still be useful in clinical settings since minimal resources are required.
