Laboratory tests for herpetic infections can be divided into (1) morphologic, (2) immunomorphologic, (3) serologic, and (4) virologic. Tzanck smears are easy to do, inexpensive, and compare favorably with cultures and immunofluorescence tests for specificity and sensitivity, but they require considerable experience to interpret accurately and they cannot differentiate between herpes type 1, herpes type 2, and varicella zoster infections. Biopsies are useful when clues to a diagnosis are being sought. Peroxidase-antiperoxidase and avidin-biotin tests present technical difficulties but interpretational difficulties are low and the results are available in a few hours. They can distinguish between herpes type 1, herpes type 2, and varicella zoster virus, as can immunofluorescence using monoclonal antibodies. Serologic tests are used primarily to distinguish between primary and recurrent herpes simplex infections. Virus isolation in tissue cultures is the gold standard for identifying herpes simplex virus but it is not 100% specific or 100% sensitive. Restriction endonuclease analysis identifies types and strains of virus by their deoxyribonucleic acid composition and it is very useful in epidemiologic studies. Ability to find virus by whatever method is influenced by the stage of the lesion. As lesions age, less infectivity and antigen result in less sensitivity of the tests.
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