What is the role of lab testing in the diagnosis of herpes simplex virus (HSV) infection?

Updated: Mar 17, 2020
  • Author: Sean P McGregor, DO, PharmD; Chief Editor: William D James, MD  more...
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Multiple modalities are available that can aid in the diagnosis of herpes simplex virus (HSV) infection. A survey of 81 public health laboratories in 2016 found that 37,101 HSV tests were performed. [44] The criterion standard for the diagnosis of HSV infection is viral culture. Detection and typing of HSV can be completed by obtaining a viral culture from unroofed skin vesicles. Early in the course of recurrent infection, 80-90% of viral cultures of untreated lesions are positive, but the false-negative rate increases after 48 hours of lesion onset.

Polymerase chain reaction (PCR) assays have become more widely available for the detection of HSV DNA. Detection and differentiation between HSV-1 and HSV-2 can be accomplished rapidly with high sensitivity and specificity, ranging from 95-99%. [45, 46] In a study comparing viral culture and PCR, HSV was detected in 31% of viral culture specimens and 53% of PCR specimens. [47] The average time for viral culture was 3 days, in comparison to 4 hours with PCR. [47] This is especially important in cases of suspected CNS infection, and PCR has replaced viral culture as the diagnostic test of choice in such cases. [48]

In the office, a Tzanck smear can be performed as a rapid test for the diagnosis of HSV infection. A Tzanck smear is prepared by scraping the floor of the herpetic vesicle. The sample may be stained with a Giemsa stain, Wright stain, or a Papanicolaou stain and then evaluated under a microscope. The presence of multinucleated giant cells is indicative of HSV infection, although the findings are not specific for the type of herpes virus. Approximately 50% of the results are positive.

Direct fluorescent antibody (DFA) testing may be used on air-dried smears, and approximately 75% of the results are positive.

Serologic assays use HSV-specific glycoproteins for detection and typing. Point-of-care and laboratory-based studies are available for HSV-2, and detection rates range from 80-98%. [48] In the early stages of infection, false-negative results may occur. [48] Serologic assays to detect antibodies against HSV-1 and HSV-2 may be useful in identifying organ transplant recipients or pregnant women who may be at risk for HSV reactivation. Their use is also becoming more common for confirming infection and for testing partners or those with asymptomatic infection. Western blot assays are highly sensitive and specific, and they can be considered in patients with suspected false-positive test results. [48]

Depending on the clinical scenario, the virus may be isolated from cerebrospinal fluid (CSF), stool, urine, the throat, anogenital mucosa, the nasopharynx, and conjunctivae. HSV-1 DNA has also been detected in tears and saliva. [49]

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