Explanation

Herpes simplex virus type 1 antibodies (HSV-1 IgG): what is measured?

Herpes simplex virus type 1 (HSV-1) is the virus that usually causes cold sores, but it can also cause genital herpes, for example after oral sex. The test looks for IgG antibodies aimed specifically at type 1, using a protein that only this type has (glycoprotein G1). These antibodies develop weeks to months after the first infection and then remain present, because the virus stays in the body for life. The test does not say where in the body the virus is, when you were infected or whether you are shedding virus at this moment.

What can it detect?

A previous infection with HSV-1, even if it never caused symptoms
Whether a first outbreak is a new infection or a flare-up of an older infection, together with a PCR test on a blister

Result

What does the result mean?

Positive result

A positive result means that you were infected with HSV-1 at some point. This is common and often already happens in childhood, through saliva or skin contact. According to the LCI guideline (RIVM), the first episode usually causes no symptoms. The virus then stays in nerve ganglia in the body and can come back from time to time as a cold sore, often with fever, sunlight, stress or menstruation. The result cannot show where the virus is located: a positive HSV-1 does not say whether you have ever had a genital infection. There is no treatment that removes the virus; symptoms during an outbreak can be treated, though.

Negative result

A negative result means that no HSV-1 antibodies have been found. After a first infection it can take weeks to months before type-specific antibodies can be detected, so shortly after an infection the test can still be negative. According to the LCI guideline (RIVM), the sensitivity of the type-specific test is between 69 and 98 percent, so some infections are missed. A negative result does not rule out genital herpes: that can also be caused by HSV-2, which this test does not measure.

After an abnormal result

With a positive result without symptoms, no treatment or monitoring is needed. With recurring symptoms, the GP can prescribe an antiviral medicine that makes an outbreak shorter. Pregnant women with a suspected first genital herpes infection are referred to a gynecologist. Herpes is not notifiable.

Reliability

How reliable is the test?

According to the LCI guideline (RIVM), the type-specific HSV-1 test has a sensitivity between 69 and 98 percent and a specificity of 92 to 95 percent. The guideline calls serology useful when it is unclear whether it is a first infection or a flare-up, but of limited value in everyday practice. With visible blisters or sores, a PCR on the fluid from the sore is the first choice. Because HSV-1 is so common, a positive result on its own says little about the cause of symptoms.

What can affect the result?

The test does not say where in the body the virus is: a positive result does not distinguish a cold sore from a genital infection.
In a first infection, type-specific antibodies can sometimes only be detected after weeks to months.
The test misses some infections and also gives falsely positive results.
The result gives no information about the moment of infection or about the chance of a next outbreak.

Who it is for

Who is the test useful for?

Useful for

The result says the most with a suspected first herpes infection where it matters whether it is a new infection or a flare-up, for example during pregnancy, and then together with a PCR on a blister. In people without symptoms, the result changes little: almost half of the population has these antibodies without being bothered by them. With visible blisters or sores, a PCR test via the GP or the GGD (municipal public health service) is better.

How common is it?

In a national population study (Pienter-2, 2006 to 2007), 42.7 in 100 inhabitants had antibodies against HSV-1; in Pienter-1 (1995 to 1996) this was still 47.7 in 100, with a drop mainly in children aged 10 to 14. Most people with HSV-1 do not notice anything of the first infection. According to the LCI guideline (RIVM), genital herpes caused by HSV-1 is more common at a younger age and in women.

LCI guideline (RIVM) on herpes simplex virus infections (Pienter study)

Drawbacks and risks

A positive result occurs in almost half of the population and says nothing about the place or moment of infection; still, it can cause worry and tension in a relationship.
A negative result can give false reassurance, because the test misses some infections and genital herpes can also be caused by HSV-2.

Get tested