Laboratory Tests

As the clinical diagnosis of genital herpes is both insensitive and non-specific, laboratory testing should be used to help diagnosis. Most clinical laboratories offer both virus detection tests and antibody detection tests.

Virus Detection

Virus detection tests begin by vigorously swabbing lesion sites to collect a viral sample. Viral detection tests include:

Culture (viable virus)

Isolation of HSV in cell culture is the preferred virologic test of most healthcare providers. Cell culture requires the collection of live virus samples that require special care in transport to the laboratory to retain viability. When viable samples are used, culture can be highly specific (if typing is performed) and positive results are generally reliable. The sensitivity of culture declines rapidly as lesions begin to heal and for this reason frequently non-positive results are falsely negative.

Antigen Detection (virus antigen)

The common methods used for antigen detection areThe common methods used for antigen detection are immunofluorescence or enzyme immunoassays. These tests are inexpensive and rapid, but have relatively low specificity and lack usefulness in asymptomatic patients.

PCR assays for HSV DNA are highly sensitive but expensive to perform.

Antibody Detection

Antibody detection or serology tests involve the detection of antibodies to HSV in the blood. Both type-specific and nonspecific antibodies to HSV develop during the first several weeks following infection and remain in the blood indefinitely. Serology tests an important adjunct to virus detection method in patients with no obvious symptoms. The following tests are in this category:

Type-common (crude antigen) serology tests measure HSV antibodies in the blood but are unable to distinguish between HSV-1 and HSV-2 infection. Most adults have HSV-1 antibodies, so crude antigen tests ability to detect HSV-2 infections is questionable.

Type-specific serology tests distinguish between HSV-1 and HSV-2 antibodies.

There are ELISA (enzyme immunoassay) tests commercially available that are type-specific assays for HSV antibodies. These tests should be based on the HSV-specific glycoprotein G2 (gG2) for HSV-2 and with glycoprotein G1 (gG1) to for HSV -1.

The HerpeSelect® tests from Focus Diagnostics are available in four formats for detecting type-specific HSV IgG antibodies.

2. HerpeSelect® ELISA consists of two micro-plate assays, one for detecting antibodies to HSV-1 (gG1), and the other for antibodies to HSV-2 (gG2).

3. Plexus™ HerpeSelect® provides both HSV-1 and HSV-2 from a single specimen using Luminex®xMAP® technology.

4. HerpeSelect® Express™ rapid HSV-2, a point-of-care device providing an HSV-2 serology result from a finger stick in about 15 minutes. (pending CLIA waiver).

All HerpeSelect assays are intended for testing sexually active adults and expectant mothers.

The Western Blot assay for HSV is highly accurate in differentiating HSV-1 and HSV-2 antibodies when used with a step to cross-adsorb antibodies to HSV-1 and HSV-2 antigens. However, it is expensive to perform, takes several days, and is not commercially available. The provider of Western blot testing services is the University of Washington.

Serological tests for HSV only indicate presence or absence of infection and do not identify the site of infection. These tests may give false-negative results in the early stages of infection because antibodies may not reach detectable levels. Repeat testing may be indicated in settings with a positive predictive value. False-positive results can also occur in patients with low likelihood of HSV infection. Repeat testing or a confirmatory test may be indicated in some cases.

Physicians can review the testing and counseling guidelines from the STD/HIV prevention programs to aid in the implementation of HSV serology testing and talking with patients.

http://depts.washington.edu/nnptc/

or

http://www.stdptc.org/