Herpes simplex virus (HSV) is one of the most common viral infections in the UK — according to NHS Lothian, around 70% of the population will have been infected with either HSV-1 or HSV-2 by their mid-twenties, though the vast majority will never know. That combination of extreme prevalence and frequent absence of obvious symptoms means that questions about testing arise naturally and often. Can herpes be diagnosed with a blood test? The answer is nuanced — a blood test can detect evidence of past exposure to the herpes virus, but it cannot diagnose genital herpes in the way many people expect, and understanding the difference matters enormously for how you interpret any result you receive.
What a Herpes Blood Test Actually Measures
A blood test for herpes does not detect the virus itself in your bloodstream. Instead, it detects antibodies — the proteins your immune system produces in response to the infection. When the herpes simplex virus enters the body, the immune system mounts a response and generates two key types of antibody:
IgM (immunoglobulin M)
The body’s initial antibody response, appearing around seven to ten days after first exposure. IgM levels peak in the early weeks of infection and then decline. A positive IgM is sometimes interpreted as indicating a recent or active infection — but IgM tests for herpes are widely regarded as unreliable. The Herpes Viruses Association UK states clearly that IgM tests can produce a false positive result in one in ten cases. They cannot accurately distinguish between HSV-1 and HSV-2, and can be triggered by other infections or even recent vaccination. For these reasons, IgM testing alone is not recommended for herpes diagnosis by most UK sexual health specialists.
IgG (immunoglobulin G)
IgG antibodies develop later — typically appearing from around two to twelve weeks after initial exposure — and remain in the blood for life. A positive IgG result indicates that you have been exposed to the herpes virus at some point in the past. Crucially, IgG testing can be done in a type-specific format — distinguishing between HSV-1 and HSV-2 antibodies using glycoprotein G-based assays — which provides more clinically meaningful information. However, as the Herpes Viruses Association UK notes, even the more accurate IgG tests can return a wrong negative result in around one in three cases, and a wrong positive in approximately one in ten.
The fundamental limitation of both antibody tests is that they cannot tell you where in the body the infection is located. As the Herpes Viruses Association UK explains clearly, having antibodies does not identify the part of the body that might be affected — only a swab of an active sore can confirm this. An asymptomatic cold sore infection around the mouth will also cause the immune system to produce antibodies, meaning a positive blood test result cannot distinguish between oral and genital herpes.
The NHS Position on Herpes Blood Testing
Understanding the NHS’s approach to herpes blood testing is important context for anyone exploring this question in the UK. NHS Lothian’s patient information states clearly: there is a blood test for herpes simplex, but it is not usual for clinics to carry it out for people who have no symptoms. This is because herpes is not usually a dangerous condition, and people who have no symptoms do not need treatment.
The UK National Screening Committee has also concluded that screening for genital herpes in the general population — or even in pregnant women — is not currently recommended. Their position, published on GOV.UK, reflects uncertainty about how many women in the UK are infected, questions about the accuracy of screening tests in pregnant women, and the absence of sufficiently effective interventions to justify a national screening programme. The NHS does not include herpes testing in the standard STI screen offered at GUM clinics unless there is a specific clinical reason to do so.
Newcastle Hospitals NHS Laboratories’ test directory confirms that the standard HSV IgG blood test identifies past exposure to HSV-1 or HSV-2 but does not differentiate between the two types and is of limited clinical utility. North Bristol NHS Trust’s guidance similarly specifies that this test is not appropriate for the investigation of current or active herpes infections. Where current or active infection needs to be confirmed, PCR testing of a sample from the affected site is the appropriate investigation — not a blood test.
When Is a Herpes Blood Test Actually Useful?
Despite its limitations, there are genuine clinical contexts in which a herpes blood test provides useful information:
Asymptomatic Exposure Concern
If you have had a sexual partner with a confirmed herpes diagnosis and want to know whether you have been exposed — but have never had any symptoms — a type-specific IgG blood test, taken at least twelve weeks after the potential exposure, can provide some indication. It should be interpreted carefully, with awareness of its false negative and false positive rates, and ideally discussed with a clinician.
Recurrent Symptoms without a Confirmed Diagnosis
If you have been experiencing recurrent symptoms that could be consistent with herpes but have never had a positive swab test, a type-specific IgG test may add useful context — though it still cannot confirm the anatomical site of infection.
Pregnancy and Neonatal Risk Assessment
Type-specific herpes serology is offered in specific clinical situations — for example, where primary HSV infection in pregnancy is a concern, or where a pregnant woman’s partner is known to have herpes. Newcastle Hospitals NHS confirms that in certain situations, such as possible primary HSV infection in pregnancy, samples can be referred for type-specific serology to differentiate between HSV-1 and HSV-2.
Pre-relationship Status Awareness
Some individuals seeking to understand their own HSV status before entering a new relationship may choose to access a private type-specific IgG test, accepting its limitations and using the result as one piece of information rather than a definitive answer.
The Gold Standard: PCR Swab Testing
If you have active symptoms — blisters, sores, ulcers, or any lesion that might be consistent with herpes — a swab taken directly from the affected site and tested using polymerase chain reaction (PCR) is significantly more accurate than any blood test. PCR testing detects the virus’s genetic material directly, rather than relying on the body’s antibody response. It is fast, highly sensitive, and can differentiate between HSV-1 and HSV-2 with precision. It can also identify the site of infection — oral versus genital — which a blood test cannot.
A PCR swab taken during an active outbreak is the most reliable method for confirming a herpes diagnosis. It is considerably more sensitive than viral culture, which can miss infections if the lesion is small or beginning to heal. For anyone presenting with active symptoms, a swab rather than a blood test should be the first step.
If you have symptoms that may indicate a herpes outbreak, a face-to-face GP consultation at The Private GP in Birmingham allows you to be assessed promptly and discreetly by a GMC-registered doctor, with access to appropriate testing and management without the potential wait or discomfort of an NHS GUM clinic. Same-day appointments are available.
Accuracy of Herpes Blood Tests: What the Research Shows
The diagnostic accuracy of herpes antibody testing has been examined in several peer-reviewed studies, and the findings reinforce why blood testing must be interpreted with care. A 2024 study published in PMC — comparing the accuracy of HSV-1 and HSV-2 IgG antibody tests with PCR in 299 patients with confirmed recurrent genital herpes — found that the accuracy of HSV-2 IgG for HSV-2 infection was just 38.1% in isolation. The combined antibody positivity accuracy was 34.9%. Even in a population where the prior probability of infection was high (given that all participants had PCR-confirmed herpes), the blood test frequently failed to return a positive result.
This is not a reason to dismiss blood testing entirely — a type-specific IgG test taken at the right time (at least twelve to sixteen weeks after potential exposure) does provide useful information. But it underlines the importance of understanding what a negative blood test result does and does not mean, and why clinical assessment and swab testing during an active episode remain the foundation of accurate herpes diagnosis.
Herpes Testing and Routine STI Screening
One point that consistently surprises people is that herpes is not included in the standard STI screening panel offered by most NHS GUM clinics or even many private STI testing services. As the Herpes Viruses Association UK notes, unless you specifically request a herpes test and the clinic offers it, it will not be included. The standard NHS STI screen at GUM clinics typically covers HIV, chlamydia, gonorrhoea, syphilis, and hepatitis B — but not herpes.
If you want to know your herpes status and have no current symptoms, you will generally need to seek out a private sexual health provider who offers type-specific HSV-1 and HSV-2 IgG testing and access it proactively. Discussing the result with a clinician who understands its limitations is essential to interpreting it meaningfully.
At The Private GP in Birmingham, we offer discreet, confidential STI testing including access to herpes antibody testing where clinically appropriate, alongside clinical consultation and sensitive, non-judgemental support. Our GMC-registered doctors will help you understand your results in full and advise on any next steps. Same-day appointments are available — book today.
What a Positive Herpes Blood Test Result Actually Means
If you receive a positive IgG result, it is important to interpret this calmly and in context. A positive HSV-1 IgG result — the more common of the two — most likely reflects exposure to the cold sore virus, which is carried by the majority of the UK population. It does not tell you whether any infection you carry is oral or genital, nor does it indicate that you are currently having an outbreak or are at a specific level of transmission risk.
A positive HSV-2 IgG result is more specifically associated with genital herpes, since HSV-2 almost exclusively affects the genital and anal regions. However, a false positive rate of around 1 in 10 — as cited by the Herpes Viruses Association UK and consistent with the 2023 US FDA advisory — means that a positive result, particularly in someone with no symptoms and low prior risk, should ideally be confirmed with a second, different test before being accepted as definitive.
Importantly, a positive herpes blood test result does not change the day-to-day health implications for most people. Herpes is a manageable condition, and the vast majority of people who carry the virus live without significant health consequences. With appropriate antiviral medication available to reduce outbreak frequency and transmission risk, and with honest, informed conversations with sexual partners, living well with herpes is entirely achievable.
Frequently Asked Questions
- Will a herpes blood test show up on a standard STI screen?
No. Herpes is not included in the standard NHS STI screening panel, and most routine STI screens — whether NHS or private — do not include herpes testing unless you specifically request it and it is available. The standard NHS GUM clinic screen covers HIV, chlamydia, gonorrhoea, syphilis, and hepatitis B. If you want to know your herpes status, you will need to ask specifically for a herpes antibody test and seek out a provider that offers it. At The Private GP, our STI testing service includes access to herpes antibody testing with clinical interpretation.
- How long after exposure should I wait before having a herpes blood test?
IgG antibodies — the more reliable antibody marker — typically take between two and sixteen weeks to reach detectable levels in the blood following initial exposure. Testing too early produces false negative results even in people who have been infected. Most sexual health specialists recommend waiting at least twelve weeks from the last possible date of exposure before having a type-specific IgG blood test for the most accurate result. If you have active symptoms at any point in that window, a PCR swab of the affected site will provide a more immediate and reliable answer.
- Can a herpes blood test tell me whether I have oral or genital herpes?
No. As the Herpes Viruses Association UK clearly states, a blood test cannot identify the part of the body that might be affected. A positive IgG result tells you that you have been exposed to HSV-1 and/or HSV-2 at some point, but not where in your body the virus is located. Since HSV-1 commonly causes oral cold sores and is carried by the majority of the adult population, a positive HSV-1 IgG result cannot be interpreted as evidence of genital herpes. Only a PCR swab of an active sore can confirm the site of infection.
- Is the herpes IgM blood test reliable?
No — and most UK sexual health specialists do not recommend relying on IgM testing for herpes diagnosis. The Herpes Viruses Association UK notes that IgM tests can return a wrong positive result in one in ten cases, cannot accurately distinguish between HSV-1 and HSV-2, and can be triggered by other infections or recent vaccination. IgM results can also mislead about how long a person has carried the virus. Type-specific IgG testing is significantly more reliable, and PCR swab testing of active lesions is the gold standard for confirming an active infection.
- Should I tell a sexual partner based on a positive herpes blood test result?
This is a personal decision, and one that benefits greatly from clinical guidance. A positive herpes blood test — particularly for HSV-1 — does not necessarily mean you have genital herpes or are a significant transmission risk. The Herpes Viruses Association UK notes that it is not required by law to disclose a positive herpes antibody result to sexual partners, though open and honest communication in sexual relationships is always advisable. Discussing your result with a GP or sexual health clinician before making decisions about disclosure will help you understand what your result actually means in your specific situation. A private GP consultation at The Private GP provides a discreet, confidential space to have this conversation.