Testing methods for sexually transmitted infections (STIs) vary widely depending on the specific pathogen being screened. While many common bacterial infections require only a urine sample or swab, herpes simplex virus (HSV), which causes oral and genital herpes, is a viral infection requiring a different diagnostic approach. The process for detecting herpes depends entirely on whether a person has visible symptoms or is seeking screening for past exposure. This article clarifies the role of herpes testing and how it differs from other routine STI screens.
Herpes Testing in Standard Screening
Herpes testing is generally not included in the standard, routine STI screening panels offered to asymptomatic individuals. Unlike chlamydia, gonorrhea, HIV, and syphilis, which are widely screened for due to their potential for severe, long-term health complications, HSV is often excluded from universal screening protocols. This exclusion is partly due to the high prevalence of the virus and the fact that testing asymptomatic people does not prevent transmission of this chronic condition.
Public health guidance often does not recommend routine screening because available blood tests have accuracy limitations, which can lead to false-positive results and unnecessary psychological distress. Therefore, individuals must typically make a specific request to their healthcare provider if they want to be tested for herpes. The provider may then order the test based on individual risk factors or clinical suspicion, rather than as part of a general panel.
Diagnosing Active Outbreaks
When a person presents with visible symptoms, such as blisters, sores, or ulcers, the diagnostic approach focuses on directly detecting the virus at the outbreak site. This is considered the most accurate way to confirm an active infection. The healthcare provider gently swabs the base of a fresh lesion to collect fluid and cells containing the virus.
The sample is sent to a laboratory for a virologic test, either a viral culture or a Polymerase Chain Reaction (PCR) test. Viral culture involves trying to grow the virus, but its sensitivity is lower, especially as lesions begin to heal. The PCR test is significantly more sensitive, as it amplifies and detects the genetic material (DNA) of the herpes virus. Because PCR allows for highly accurate identification and can differentiate between herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), it is often the preferred method for diagnosing an active outbreak.
Antibody Testing for Asymptomatic Status
For individuals without symptoms who want to check for past exposure, a blood test is used to detect antibodies. This test looks for immunoglobulin G (IgG) antibodies, which the immune system creates in response to an HSV infection and persist indefinitely in the bloodstream. A positive IgG result confirms past exposure and indicates a lifelong infection, though it cannot determine the exact location of the infection or if an outbreak is currently occurring.
The most reliable serologic tests are type-specific, looking for antibodies to glycoprotein G1 (gG1) for HSV-1 and glycoprotein G2 (gG2) for HSV-2. Distinguishing between the two types is important because HSV-2 causes most recurrent genital infections, while HSV-1 is increasingly responsible for primary genital infections. Early antibody tests, such as those looking for IgM antibodies, are generally not recommended because they are not type-specific and do not reliably indicate a new infection.
Understanding Test Results and Timing
The timing of a blood test for herpes antibodies is important for ensuring an accurate result. After initial exposure, the body requires a “window period” to produce detectable levels of IgG antibodies. This seroconversion period typically lasts from three to six weeks, but can take up to three to six months for antibodies to fully develop.
Testing too early during this window period can lead to a false negative result. For this reason, a repeat test is often recommended several weeks after a suspected exposure if the first result is negative. Furthermore, in low-risk populations, a positive result may have a low positive predictive value, occasionally warranting a confirmatory test.
Test results are typically reported as positive, negative, or indeterminate (equivocal). An indeterminate result means the antibody level is borderline and cannot definitively be classified. In this situation, the healthcare provider usually recommends repeating the test after several weeks to allow antibody levels to rise to a detectable threshold.