How Accurate Are Herpes Blood Tests?

Written by: Sendra Yang, PharmD, MBA

Herpes is a very common viral infection that can spread easily.[1] There are two types: oral herpes and genital herpes. Genital herpes is a sexually transmitted infection (STI) that affects millions of people.[1] According to the US Centers for Disease Control and Prevention (CDC), an estimated 572,000 new genital herpes infections occurred in 2018 among people between the ages of 14 to 49 years old. Since herpes can be transmitted without symptoms, detection through herpes testing is essential for diagnosis, treatment, and prevention. Continue reading to explore the different types of herpes tests, how accurate they are, and what factors can impact herpes test results.

How Accurate are Herpes Blood Tests?

When talking about herpes blood test accuracy, two important terms to understand are sensitivity and specificity. These terms help to measure and describe how well a medical test, such as the herpes test, works.[5] In other words, the terms help us measure how well a test works in detecting herpes. The currently recommended herpes tests have high sensitivity and specificity, so they can correctly identify who has herpes and who does not [2]:

• Sensitivity is how good a test is at detecting the disease in people who have the disease.[3-5] Sensitivity in herpes tests will tell us how well it detects herpes in the infected people. For example, if a test has a 90% sensitivity, it means that out of 100 people who have the disease, 90 people will be identified as having the disease, while 10 will be missed. The people misidentified as not having the disease when, in fact, they did is known as false negatives.
• Specificity tells us how good a test is at detecting people who do not have the disease.[3-5] In herpes tests, specificity will tell us how well it identifies people who do not have herpes and are not infected. For example, if a test has 95% specificity, it means that out of 100 people who do not have the disease, the test correctly identifies 95 of them as healthy but wrongly says 5 have the disease when, in fact, they do not. The people misclassified as having the disease when they do not are known as false positives.

A highly sensitive test helps detect as many actual cases as possible, while a highly specific test helps avoid misdiagnosing people as having the disease when they do not.

Herpes Testing

Herpes testing is important for finding out if someone has herpes, especially if they have symptoms or think they were exposed.[1,2] There are two main ways to test for herpes: tests that detect the virus itself and tests that detect herpes antibodies in the blood.[2,3] Based on the initial test, a confirmatory could be used to confirm the diagnosis and infection with either HSV-1 or HSV-2 [2,4]:

Some tests detect the herpes virus. These tests look for the actual herpes virus in a sample taken from a sore or lesion [2]:

• HSV Nucleic Acid Amplification Testing (NAAT) assay: This detects the herpes simplex virus from genital ulcers or lesions.[2,3] A sample is taken from a herpes sore and sent to a lab to check for the virus. This test works best when the sore is fresh but is less accurate once it starts healing. HSV detection assays vary in sensitivity from 90.9% to 100% and are considered highly specific.[2]
• Polymerase Chain Reaction (PCR) test: This test can look for the herpes virus's genetic material in a sample from a sore, blood, or spinal fluid.[2,3]
• Viral Culture: This test grows the herpes virus in a lab.[2,3] The sensitivity of viral culture is low, especially if lesions recur often or are beginning to heal.[2,3]

Other tests detect herpes antibodies: These blood tests look for antibodies made by the immune system to help fight the herpes virus [2]:

• Type-Specific Antibody Tests: These tests detect antibodies against HSV1 and HSV2 and help distinguish between the two types.[2-4] Type-specific serologic tests detect antibodies against proteins on the herpes viruses, allowing for accurate identification of the infecting virus type.[2,3] It's important to consult a healthcare provider to determine if type-specific herpes testing is appropriate based on individual risk factors and clinical presentation.[2]

Interpreting Results

Understanding herpes test results depends on the type of test used.

PCR Tests

• If a PCR test or viral culture comes back positive, it means the herpes simplex virus is present, confirming an active infection.[2,5]
• If the result is negative, it does not always mean the person is herpes-free—especially if the test was done too late when the virus is no longer detectable on the skin.[5] False negatives can happen if the sample was not taken properly or if the virus was not actively shedding at the time of testing. For this reason, healthcare providers may recommend repeat testing if symptoms continue. In these cases, your healthcare provider may order a confirmatory test.[2]

Antibody Tests

For antibody tests, results show whether a person has ever been infected with HSV.[2]

• A positive antibody test means the immune system has created defenses against the virus, indicating a past or current infection.[2,3,5] HSV-1 and HSV-2 antibodies can help determine which type of herpes a person has, but these tests cannot tell if the infection is active or when it happened.
• A negative antibody test usually means the person has never been exposed to HSV. Still, if the test was taken too soon after exposure, the body may not have had enough time to produce detectable antibodies.

Factors Affecting Test Results

Several factors affect herpes test results.[1-6] Because of these limitations, healthcare providers use test results alongside symptoms and medical history to make accurate diagnoses:

1. Timing of the test [2,3,6]: Viral culture and PCR tests are most accurate within 72 hours of an active outbreak. If a sore has started to heal or the sample is taken too late, the virus may no longer be detectable. Antibody herpes tests taken too soon after exposure may not have time for the body to make enough detectable antibodies.
2. Type of herpes test used [2,5]: The various herpes tests have varying degrees of sensitivity and specificity. PCR tests are highly sensitive and can detect small amounts of herpes virus, making them more reliable than viral culture tests, which may give false negatives.
3. Sample collection method [2-6]: Proper sample collection is essential for accurate results. If not enough virus is collected in the sample, if the area is cleaned before testing, or if the sample is improperly handled or contaminated, results may not be accurate.
4. Other infections and conditions [1,2,6]: [Co-existing STIs](https://www.everlywell.com/blog/sti-testing/syphilis-vs-herpes/), especially HIV, can impact herpes test outcomes because the immune system may be impacted, altering antibody production and affecting test results.

What to Do After Herpes Testing

If a herpes test comes back positive, it is essential to talk to a healthcare provider about treatment and ways to prevent spreading the virus.[1,2] Repeat testing may be needed for individuals who test negative but still have symptoms.[1,2] Follow-up testing can confirm the results, especially if the first test was done too soon after exposure. Since herpes is an STI, it is also a good idea to get tested for other STIs like gonorrhea, chlamydia, syphilis, and HIV.

Take Control of Your Health Today with Everlywell

At Everlywell, several STI tests are available for you to test for common STIs from the comfort of your home—discreetly, conveniently, and at an affordable cost. All EverlyWell tests are data-secured and reviewed by physicians. If your results indicate a need for further treatment, you'll be connected to a care provider who can help you decide the best course. Additionally, with our virtual care services, you can even meet with a licensed clinician to receive genital herpes treatment online.

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References

1. About genital herpes. Centers for Disease Control and Prevention. Accessed February 14, 2025. Medical Citation URL.
2. Herpes - STI treatment guidelines. Centers for Disease Control and Prevention. September 21, 2022. Accessed February 14, 2025. Medical Citation URL.

<li><font size="-1">Asher GN, Feltner C, Harrison WN, Schwimmer E, Rains C, Jonas DE. Serologic Screening for Genital Herpes: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force. <a href="JAMA. 2023;329(6):510-512."_blank" rel="noopener noreferrer"> Medical Citation URL. </a></font></li> 

3. Arshad Z, Alturkistani A, Brindley D, Lam C, Foley K, Meinert E. Tools for the diagnosis of herpes simplex virus 1/2: systematic review of studies published between 2012 and 2018. Medical Citation URL.

<li><font size="-1">Maxim LD, Niebo R, Utell MJ. Screening tests: a review with examples. <a href="Inhal Toxicol. 2014;26(13):811–28.

"_blank" rel="noopener noreferrer"> Medical Citation URL.

<li><font size="-1">Mathew Jr J, Sapra A. Herpes Simplex Type 2. [Updated 2024 March 13]. In: StatPearls [Internet].2025 Jan. <a href="https://www.ncbi.nlm.nih.gov/books/NBK554427/"_blank" rel="noopener noreferrer"> Medical Citation URL. </a></font></li> 

Sendra Yang received her Doctor of Pharmacy and Master of Business Administration degrees from Wingate University School of Pharmacy. She is a skilled medical information professional with experience in the pharmaceutical industry, pharmacy education, and clinical practice. She has also been a medical writer and editor for consumer health and medical content. Sendra is passionate about translating complex medical concepts into simple and easy-to-understand information.