How is a Tzanck smear performed?

In a Tzanck smear, the base of the suspected herpetic lesion is gently scraped, and the skin or mucosal cells removed are placed on a glass slide. The cells are stained and then examined by light microscopy for evidence of viral-induced cytologic change, including the characteristic multinucleated giant cells. Tzanck smears provide an efficient and inexpensive method of diagnosis, although the results are not always definitive. This technique cannot distinguish HSV-1 from HSV-2 or HSV from VZV.