Which test is most sensitive and specific for diagnosing herpes simplex virus infection?

• A. Tzanck smear
• B. Serology
• C. PCR for HSV
• D. Viral culture

Answer: (C)

Detecting herpes simplex infection most accurately comes from identifying the virus itself rather than the body’s response. Polymerase chain reaction (PCR) for HSV directly detects viral DNA and offers the highest sensitivity and specificity, making it the best choice for confirming active infection in lesions or in cerebrospinal fluid when HSV encephalitis is suspected.

Tzanck smear is rapid but unreliable: it shows multinucleated giant cells without distinguishing HSV from other viruses like varicella-zoster, and its sensitivity is lower. Viral culture can identify HSV but is slower and less sensitive, especially if the sample isn’t ideal or after antiviral therapy. Serology reveals antibodies indicating past exposure rather than current infection, so it’s not the best for acute diagnosis.

So, PCR for HSV stands out as the most accurate test for diagnosing active HSV infection.