Many challenges face clinicians regarding the use of genital herpes laboratory tests, especially in the area of serologic test selection and timing of use. The following are important points to consider when selecting a test:
- Viral detection methods are the best methods for diagnosing genital herpes when lesions are present. However, due to declining sensitivity of viral culture as lesions begin to heal, a negative culture result does not rule out genital herpes.4 PCR tests provide a more sensitive alternative for both lesion and skin testing but are not 100% sensitive, can be more costly, and are not readily available in all locations. In either case, to accurately detect virus, the skin must be swabbed vigorously to obtain infected cells and the sample must be placed in the proper collection vial and transported under appropriate conditions. If the swab test is negative or not performed, a serologic test may be the next step.
HSV DNA tests are another option with symptomatic patients. These assays are highly sensitive, accurately distinguish HSV-1 from HSV-2, and usually offer quicker turnaround than viral culture.
- The type-specific serologic tests, while generally accurate, can only detect HSV antibodies after a person’s immune response has made detectable antibody. Some patients develop antibodies a few weeks after lesions appear. Others require six weeks, and nearly all will develop antibodies by 16 weeks.9 The most sensitive tests for detection of early seroconversion include the Focus HerpeSelect® ELISA and biokit HSV-2 Rapid test. By three months, 93% of patients infected with HSV-2 will have seroconverted as measured by HerpeSelect.®Older, serologic tests that are not type-specific are inaccurate and should never be ordered.10
- Type-specific serologic tests detect IgG (Immunoglobulin G) antibodies. The current STD Treatment Guidelines from the Centers for Disease Control and Prevention (CDC) state that accurate, type-specific assays for HSV-1 and HSV-2 should be based on HSV type-specific glycoprotein G (gG).4 Currently available IgM serologic tests can be falsely positive and should not be used to diagnose genital herpes.11
- Type-specific serologic tests provide qualitative results. Thus, the exact value does not relate to the severity, recency, or other clinical characteristics of the individual’s infection.