A herpes blood test detects IgG antibodies to herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) — not the virus itself. Positive antibodies mean your immune system has been exposed to that strain of herpes at some point in the past. Blood-based IgG testing is most useful for people without active symptoms who want to understand their HSV status. For active sores or lesions, a PCR swab of the affected area is more accurate for diagnosis.
Types of herpes blood tests
| Test Type | What It Detects | When It Is Used |
|---|---|---|
| HSV-1 IgG | Antibodies to herpes simplex virus type 1 | Serologic status check; most common cause of oral herpes (cold sores) |
| HSV-2 IgG | Antibodies to herpes simplex virus type 2 | Serologic status check; primary cause of genital herpes |
| HSV-1/2 IgG combo | Antibodies to both strains, with differentiation | Standard panel when both strains are being assessed |
| PCR swab (active lesion) | HSV DNA directly from an active sore | Diagnosing an active outbreak; most accurate during active symptoms |
| Western blot (confirmatory) | Highly specific antibody confirmation | Confirming low-positive IgG results (index value 1.1–3.5) |
Note: IgM antibody tests for herpes are not recommended. They are unreliable — they can be positive during reactivations of either strain, not just primary infection, and produce high false-positive rates. The CDC and most labs recommend IgG testing only.
How the IgG test works
When your body encounters HSV for the first time, it mounts an immune response that includes producing IgG antibodies specific to that strain. These antibodies remain in your bloodstream indefinitely — they are the immune system's "memory" of the infection.
The standard commercial test (HerpeSelect, developed by Focus Diagnostics) reports results as an index value:
- Below 0.9: Negative — no detectable antibodies
- 0.9–1.1: Equivocal — borderline; repeat testing recommended
- 1.1–3.5: Low positive — confirmed by most labs as positive, but false-positive rate in this range is higher (up to 20–50% in some low-prevalence populations); confirmatory Western blot recommended
- Above 3.5: Positive — true positive rate is very high
Accuracy and limitations
The HerpeSelect HSV-2 IgG test has approximately 97% sensitivity (correctly identifies 97% of infected people) and 98% specificity (correctly identifies 98% of uninfected people) when performed more than 12 weeks after exposure.
Important limitations to understand:
- Window period: IgG antibodies typically become detectable 12–16 weeks after initial infection. Testing too early after a potential exposure can produce a false negative. If your test is negative and you had a recent exposure, retest at 12–16 weeks.
- Low-positive index values: Results between 1.1 and 3.5 have meaningfully higher false-positive rates, particularly in populations with low HSV-2 prevalence. If you receive a low-positive result and are uncertain, the University of Washington's Western blot test is the most accurate confirmatory test available.
- No location information: A blood test cannot tell you where the infection is located — oral, genital, or both. HSV-1 causes genital herpes more often than previously recognized, and an HSV-1 IgG positive result does not confirm oral infection specifically.
- No timing information: A positive result does not tell you when you were infected or from whom. Some people carry HSV-1 or HSV-2 for years without knowing it.
HSV-1 vs. HSV-2: what the test tells you
Both HSV-1 and HSV-2 cause herpes, but their typical locations and transmission patterns differ:
- HSV-1 most commonly causes oral herpes (cold sores, fever blisters) and is extremely prevalent — approximately 67% of adults under 50 worldwide carry HSV-1 antibodies, most acquired in childhood. HSV-1 can also cause genital herpes, and its incidence in that location has increased significantly in recent decades, particularly among younger adults.
- HSV-2 is the primary cause of genital herpes. In the U.S., approximately 12% of adults between 14 and 49 carry HSV-2 antibodies (CDC, 2018 estimate). HSV-2 is transmitted almost exclusively through sexual contact.
A positive HSV-1 IgG without any genital symptoms most likely reflects prior oral herpes exposure. The clinical significance of an HSV-1 IgG positive depends on context — your provider can help interpret what a positive result means for your specific situation.
When a blood test is the right choice vs. a swab
| Situation | Better Test |
|---|---|
| Active sore, blister, or lesion currently present | PCR swab of the active lesion (more accurate) |
| No active symptoms; want to know HSV status | IgG blood test |
| Partner has known herpes; want to know your status | IgG blood test (wait at least 12–16 weeks after last exposure) |
| Routine STI screening | Request IgG blood test specifically (not included automatically in most STI panels) |
| Low-positive IgG result, want confirmation | University of Washington Western blot (confirmatory) |
Does a standard STI panel include herpes?
Most standard STI panels — whether ordered by a primary care provider or at a testing center — do not include HSV IgG testing by default. Standard panels typically cover gonorrhea, chlamydia, syphilis, and HIV. You must specifically request herpes antibody testing if you want it included.
The CDC does not recommend routine herpes blood screening for asymptomatic adults in low-risk populations, primarily because of the psychological impact of low-positive results and the limitations described above. However, testing is appropriate when there is clinical concern, a known exposure, or a specific request.
Getting a herpes blood test at home
An HSV IgG blood test requires a standard venous blood draw. A mobile phlebotomist can come to your home to collect the specimen, which routes to Quest Diagnostics, Labcorp, or your provider's preferred lab for processing. Results are typically available within 2–3 business days.
You will need a provider order to access IgG testing through a reference lab. If you do not have an order, your primary care provider, OB/GYN, or a telehealth provider can place one.
Understanding your result: positive, negative, or low-positive
When you receive your IgG result, the report shows an index value, not just a positive or negative label:
- Negative (below 0.9): No detectable IgG antibodies. Either you have not been exposed to HSV-2 (or HSV-1 for the type tested), or you were infected very recently and antibodies have not yet developed. Repeat at 12–16 weeks if there was a recent potential exposure.
- Equivocal (0.9–1.1): Borderline result. Repeat testing in 2–4 weeks is recommended to confirm whether the value moves into clearly negative or positive territory.
- Low-positive (1.1–3.5): This range has the highest false-positive rate in populations where HSV-2 prevalence is low (under 10%). Confirmatory testing with the University of Washington Western blot is recommended before accepting this result as a true positive, especially in low-risk individuals.
- Positive (above 3.5): High likelihood of true positive. False positives above this index value are uncommon but not impossible. Your provider will interpret this in the context of your symptom history and risk factors.
A positive result requires a clinical conversation — not just a lab report. The implications for your health, disclosure decisions, and partner testing are significant enough that results should always be reviewed with a healthcare provider, not just read from a portal notification.
STI panel drawn at home
A certified Speedy Sticks phlebotomist collects your blood draw at home. Request HSV IgG testing specifically when booking with your provider's lab order.
Book a visit →