Viral culture is considered the gold standard for HSV diagnosis. It is the preferred test if genital ulcers or other mucocutaneous lesions are present. Viral culture is highly specific (>99%), but sensitivity depends on stage of lesion and proper collection technique and declines rapidly as lesions begin to heal. Viral recovery for early vesicles is about 90%, for ulcers about 70%, and for crusted lesions about 30%.

Culture is more commonly positive in primary infection (80%–90%) than with recurrences (30%). Most cultures will be positive within 24-72 hours.

Antigen detection is fairly sensitive (>85%) in symptomatic shedders and may be better than culture for detecting HSV in healing lesions. Antigen detection is rapid (2-12 hours) and highly specific, but false positives can occur.  The direct fluorescent antibody (DFA) test distinguishes between HSV-1 and HSV-2, while other virologic tests do not.

Cytology (Tzanck or Pap) identifies typical HSV-infected cells (multi-nucleated giant cells and eosinophilic inclusion bodies) in exfoliated cells or biopsies. Cytologic detection of cellular changes resulting from HSV infection is insensitive (50%) and nonspecific. It should not be relied upon for HSV diagnosis, either for genital lesions (i.e., Tzanck preparation) or for cervical Pap smears.

Polymerase Chain Reaction (PCR) assays for HSV DNA are highly sensitive and specific, however PCR tests are not FDA-cleared for testing of genital specimens, are not widely available, and may lack standardization across laboratories. PCR is the preferred test for detecting HSV in spinal fluid.

The following table shows a comparison of the virologic tests

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