Herpes (HSV) 2 IgG Test · Blood

Most people who carry herpes simplex virus type 2 never know it. Roughly 80% of those infected have no recognized symptoms, yet they can still transmit the virus to partners, and infection permanently raises the risk of acquiring HIV. A standard STI screening panel typically does not include this test, which means you can get a clean bill of health from routine testing while unknowingly carrying the virus.

HSV-2 IgG (herpes simplex virus type 2 immunoglobulin G) is a blood antibody test that answers one question: has your immune system ever encountered HSV-2? Unlike a swab test that looks for the virus itself during an active outbreak, this blood test detects the long-lasting antibodies your body builds after infection. Those antibodies persist for life, so a positive result means you have been infected at some point, whether or not you have ever noticed a sore.

How Common Is HSV-2?

HSV-2 is one of the most widespread sexually transmitted infections on the planet. Global estimates suggest about 13% of people aged 15 to 49 are infected, with higher rates in women and in sub-Saharan Africa. In the United States, seroprevalence (the percentage of people who test positive on a blood antibody test) has been roughly 12 to 17% in recent national surveys. In Europe and parts of Asia, the figure is similar, around 7 to 12%.

Among people living with HIV, HSV-2 seroprevalence can exceed 45 to 70%. This overlap is not a coincidence, and it points to one of the most consequential findings about this virus.

HSV-2 and HIV Risk

The link between HSV-2 infection and HIV is the single most studied and clinically significant association for this test. If you carry HSV-2, your risk of acquiring HIV is roughly two to five times higher than someone who is HSV-2 negative. That number comes from multiple large meta-analyses spanning decades of research across different populations.

Sources: Freeman et al. 2006 (19 studies); Looker et al. 2017 (57 studies); Wald & Link 2002 (9 prospective studies).

What this means for you: if you are HSV-2 positive and sexually active, especially in settings where HIV is common, knowing your status lets you and your partners take concrete steps to reduce HIV transmission risk. If you are HSV-2 negative, a result confirms that this particular vulnerability does not apply to you right now.

Dementia Associations

A growing area of research has explored whether herpes viruses, including HSV-2, contribute to later-life cognitive decline. The evidence is mixed but worth understanding.

In a Swedish study of 1,002 adults aged 70 followed for 15 years, those who carried anti-HSV IgG antibodies (a combined measure of HSV-1 and HSV-2, not specific to HSV-2 alone) had about twice the risk of developing dementia compared to those who did not, even after adjusting for sex, education, and APOE e4 (a gene variant linked to Alzheimer's risk). A much larger Korean study of 752,205 adults followed for up to 11 years found that a clinical herpes diagnosis was associated with about 38% higher dementia risk. However, a 2025 meta-analysis pooling 32 studies found that while clinical herpes episodes showed a modest link to dementia (about 36% higher risk), the association weakened or disappeared when researchers looked only at blood antibody results like this test.

The takeaway: HSV infection may play a role in dementia risk, but the connection is far from settled. A positive HSV-2 IgG result alone is not a reason to worry about cognitive decline. If dementia runs in your family and you also test positive, it may be one more reason to stay aggressive about the modifiable risk factors (exercise, blood pressure, blood sugar) that have a much clearer evidence base.

Blood Sugar and Metabolic Risk

One well-designed German study (the KORA cohort) followed 1,257 adults with normal blood sugar for about seven years and found that HSV-2 seropositivity was independently associated with developing pre-diabetes or diabetes. The association survived adjustment for an extensive set of confounders including BMI, physical activity, fasting glucose, and insulin resistance. This is a single cohort finding, not yet replicated at scale, so it signals an area to watch rather than a firm conclusion.

Understanding Your Result

This test is fundamentally different from most biomarkers. There is no "optimal range" to aim for. The result is essentially binary: you either carry antibodies to HSV-2 or you do not. Modern type-specific tests targeting a surface protein called glycoprotein G (gG-2) are highly accurate, with sensitivity (ability to catch true positives) of 92 to 100% and specificity (ability to correctly clear true negatives) of 97 to 100%, depending on the assay.

Your lab will report an index value along with an interpretation. The exact scale depends on the assay, but the general framework looks like this:

Exact cutoff values differ by manufacturer. For example, one widely used assay (Euroimmun) uses a threshold of 22 RU/mL. Others use index values where 1.1 or above is positive. Always interpret your result using the reference range printed on your specific lab report.

The Low-Positive Problem

The most common source of confusion with this test is the low-positive result. On some commercial assays, index values in the range of roughly 1.1 to 3.5 have a false-positive rate as high as 50% when checked against more definitive testing (Western blot, a laboratory method that separates and identifies specific proteins to confirm the presence of HSV-2 antibodies). This means that about half the people who receive a low-positive result on a standard screening test may not actually be infected.

Research using a more sensitive laboratory method (flow cytometry) confirmed that many samples classified as "indeterminate" by Western blot were clearly negative, representing background immune reactivity rather than true HSV-2 infection. If your result falls in this low-positive zone, a confirmatory test is essential before concluding you are infected.

When Results Can Be Misleading

A few situations can produce results that do not reflect your true infection status:

• Window period: After a new HSV-2 infection, it can take several weeks (and occasionally up to 12 weeks) for IgG antibodies to reach detectable levels. Testing too soon after exposure can produce a false negative.
• HSV-1 cross-reactivity: Some older or less specific assays can partially cross-react with HSV-1 antibodies (mistaking one type for the other), producing a false positive for HSV-2 in someone who only carries HSV-1. Modern gG-2 based tests minimize this, but it remains a concern with certain platforms.
• Assay variation: Different commercial tests use different antigens and cutoff values. A result that is positive on one platform may be equivocal on another. Comparing results across different labs or assays is unreliable.

Common medications (statins, metformin, thyroid drugs, blood pressure medications, proton pump inhibitors) do not affect HSV-2 IgG results. Acute events like exercise, illness, or food intake in the hours before your blood draw also do not distort this test. The antibodies it measures change over weeks to months, not hours.

Why IgM Testing Is Unreliable for Timing

A common misconception is that HSV IgM antibodies (a different antibody class from IgG) can tell you whether an infection is recent. In practice, IgM is detected in about 30% of people with long-established HSV-2 infections, and it is frequently positive during recurrences, not just during the first episode. Multiple studies have concluded that IgM adds little value for distinguishing new from old infection in routine care. If your provider orders IgM alongside IgG, understand that a positive IgM does not reliably mean your infection is new.

When and Why to Retest

Because HSV-2 IgG is a permanent marker once truly positive, serial trending works differently than for metabolic biomarkers. You are not tracking a number that goes up and down with lifestyle changes. Instead, retesting serves specific purposes.

If your result is negative and you remain sexually active, retesting every one to two years (or sooner after a new partnership or potential exposure) can catch a new infection that the first test missed. If your result is in the low-positive or equivocal range, retesting with a different assay or a confirmatory method like Western blot is the next step. A clearly positive result (high index value, well above the cutoff) on a validated type-specific test does not need to be repeated. Once confirmed, the result is definitive and lifelong.

What to Do With Your Result

A confirmed positive result does not change what has already happened, but it opens the door to meaningful action. Suppressive antiviral therapy (acyclovir or valacyclovir) reduces viral shedding (the release of virus from the skin even when no sore is visible) by roughly 70 to 80% in clinical trials, which lowers both your recurrence frequency and the risk of transmitting the virus to partners. If you are pregnant or planning to become pregnant, knowing your HSV-2 status is especially relevant because it guides decisions about preventive antiviral treatment near delivery to protect the baby from neonatal herpes.

Because of the strong HSV-2 and HIV connection, a positive result is also a prompt to make sure your HIV testing is current and to consider additional protective measures if you are in a higher-risk context. Pair this test with a full STI screen (HIV, syphilis, chlamydia, gonorrhea, hepatitis B) to get the complete picture.

A negative result is reassuring but not permanent. If your sexual risk profile changes, retest. And if your result is equivocal or low-positive, do not accept it at face value. Request confirmatory testing through a different method before making any clinical or personal decisions based on the result.