Genital Herpes Tests: When Can Results Be Misleading?

Why can a herpes blood test give a false-positive result?

The FDA's October 1 warning letter to Amazon about unapproved genital herpes products emphasized that effective treatment requires professional diagnosis and supervision. For consumers, that raises a related practical issue: understanding what a herpes test actually establishes. A product advertisement, symptom checklist, or isolated laboratory result cannot provide the same assessment as a clinical evaluation. [FDA warning letter](https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/amazoncom-inc-736006-10012026).

The FDA addressed testing accuracy separately in a December 2023 safety communication. It warned that HSV-2 blood tests can incorrectly indicate infection, with particular concern about results close to the positive threshold and testing people whose likelihood of infection is low. The agency recommends explaining these limitations before testing and confirming reactive results according to the test's instructions and professional guidance. Confirmation may involve a different method, such as Biokit or Western blot. An initial result therefore needs interpretation alongside symptoms, exposure history, and the specific assay used. [FDA testing safety communication](https://www.fda.gov/medical-devices/letters-health-care-providers/hsv-2-tests-genital-herpes-can-produce-false-reactive-results-letter-clinical-laboratory-staff-and).

Which herpes test is most useful when genital sores appear?

When a person has genital blisters or ulcers, clinicians can collect material directly from a lesion and test it for herpes simplex virus. PCR is one type of nucleic acid amplification test, or NAAT, which detects viral genetic material. Identifying HSV-1 or HSV-2 also helps inform counseling because their patterns of recurrence differ. A negative swab does not always exclude herpes, especially when a lesion is older or viral shedding is intermittent. [CDC herpes diagnostic guidance](https://www.cdc.gov/std/treatment-guidelines/herpes.htm).

Assessment also needs to consider other causes. The CDC cautions that medical history and appearance alone can misidentify genital ulcers; herpes and syphilis can even occur together. Evaluation may therefore include syphilis and HIV testing as well as herpes testing. When a clinician suspects a first episode of genital herpes, treatment may begin while results are pending because prompt therapy matters. Seeking care while sores are present creates an opportunity to obtain an informative sample and address symptoms without unnecessary delay. [CDC genital ulcer guidance](https://www.cdc.gov/std/treatment-guidelines/genital-ulcers.htm).

Should people without symptoms get a herpes blood test?

In its February 2023 recommendation, the U.S. Preventive Services Task Force advised against routine herpes blood screening in adolescents and adults without a known history, signs, or symptoms, including during pregnancy. Its evidence assessment found that the harms of population screening outweigh the benefits. False-positive diagnoses can cause emotional distress, disrupt relationships, and lead to unnecessary treatment. This recommendation concerns routine screening; people seeking evaluation for suggestive symptoms, and those with HIV or other immunosuppressive conditions, require a different assessment. [USPSTF screening recommendation](https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/genital-herpes-serologic-screening).

The CDC identifies circumstances in which blood testing may help, including having a partner with genital herpes or having symptoms that need clarification. Timing matters because tests may not detect a recently acquired infection immediately. Patients can ask which test is being ordered, whether a positive result will need confirmation, and whether follow-up testing could be necessary. They should also check which infections an STI panel includes: a request to test for everything does not guarantee that herpes testing was performed. [CDC patient testing guidance](https://www.cdc.gov/herpes/testing/index.html).