Herpes Testing
An IgG blood test is used to diagnose herpes simplex virus (HSV) infection.
This test does not detect the virus. Rather, it detects the IgG antibodies, or immune proteins, that your body produces in response to the viral infection.
Parts of the IgG protein, like all antibodies, are made by the immune system to attack specific disease-causing organisms (pathogens), like viruses and bacteria. HSV IgG is the type of antibody that is produced when a herpes infection occurs.
An HSV IgG test is typically used to confirm a genital herpes infection. It is not recommended as a general screening test for everyone. But it is recommended for pregnant women who are at risk of having genital herpes. Treatment can reduce the risk of transmission to the baby.
Notes:
- The Centers for Disease Control and Prevention (CDC) currently advises against HSV testing for people without symptoms. Doing so has not been shown to change sexual behaviors. It also doesn't reduce the rate of herpes transmission.
- It can take three to six weeks from the initial infection before enough IgG is produced to be detected.
IgG vs. IgM:
The IgG test is not the only antibody test used to detect HSV. There's also an HSV immunoglobulin M (IgM) test, which detects IgM.
Unlike IgG antibodies that stay in the body and can be detected for a lifetime, IgM antibodies don't last very long. They usually can only be detected during an active or recent infection.
Another advantage of the IgG test is that it's more accurate when it comes to telling the difference between HSV-1 and HSV-2:
- HSV-1 is the type of herpes primarily associated with cold sores.
- HSV-2 is the type that mainly causes genital herpes.
If you have clinical signs of an infection and your HSV IgG test is negative, repeat the test in about four to six weeks to confirm the results.
An HSV test with a positive (abnormal) IgG result means that you either have or have had an HSV infection at some point. Since a positive result means that your body has built an IgG immune response to HSV, a negative IgG test means that your body has never needed to do so and you have never been infected with HSV.
The results of your HSV blood test will generally be reported as either:
Positive: IgG detected
Negative: IgG not detected
Equivocal: Results unclear
If your test is equivocal, your healthcare provider might consider results of other tests you've had done to make your diagnosis. They might also recommend that you repeat the IgG test after a few weeks.
IgG results may be considered along with IgM results. IgG antibodies take longer to produce but last a lifetime. IgM antibodies are detectable after a few days, but they disappear within a few weeks.
- If you test positive for IgG and IgM, or just IgM, it's likely that you have a new infection.
- If you test positive for IgG but not IgM, you likely have an existing infection that has been around for at least two months.
That said, between 30% and 70% of people with recurrent infections test positive for IgM.
A false-negative result, in which your test result is incorrectly reported as negative for HSV antibodies, can sometimes occur. This happens, for instance, if you have your test within the window period, not allowing enough time to pass after a possible exposure. You may also have a false-positive result, in which the test result incorrectly reads as positive.
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Biomarkers included in this panel:
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