Explanation

Parvovirus B19 IgG: what is measured?

Parvovirus B19 causes fifth disease, a childhood illness with red cheeks and a spotty rash. The virus spreads through coughing and sneezing. After an infection, the immune system first makes IgM antibodies and then IgG antibodies (immune proteins). According to the LCI guideline (RIVM), IgG antibodies remain present for a long time and go together with protection against a new infection. This test measures only IgG and therefore says something about an infection in the past, not about an infection right now.

What can it detect?

A past infection with parvovirus B19 and the protection that goes with it
A lack of protection, which matters mainly during pregnancy, with anemia or with a weakened immune system

Result

What does the result mean?

Positive result

IgG antibodies were found. This means you have had the infection before, often as a child and often without noticing. According to the LCI guideline (RIVM), these antibodies protect against a new infection. For a pregnant woman with a positive result, contact with someone with fifth disease poses no extra risk to the baby. The result says nothing about symptoms right now: if the picture fits a recent infection, IgM or a PCR test is also needed.

Negative result

No IgG antibodies were found. You have then probably not had the infection and can still get it. In adults, the infection more often causes joint symptoms than a rash, especially in women, and these can last for months. During pregnancy, a first infection can give the baby anemia: according to the LCI guideline (RIVM), the chance of severe fluid build-up in the baby (hydrops) in the first 12 weeks is 5 to 10 in 100 and smaller after that, and the chance of a miscarriage with infection before week 20 is about 10 to 15 in 100. In people with congenital anemia or a weakened immune system, the virus can cause a temporary, sharp drop in the number of red blood cells.

After an abnormal result

In a pregnant woman without detectable antibodies after contact with fifth disease, the test is usually repeated after a few weeks, together with IgM and a PCR test; if there are signs of infection, monitoring with ultrasound scans by the gynecologist follows, and treatment of the baby if needed. In people with anemia or a weakened immune system, the blood count is monitored. Individual cases are not notifiable; with two or more cases in an institution, reporting is mandatory.

Reliability

How reliable is the test?

According to the LCI guideline (RIVM) on parvovirus B19 infection, IgG is the test for finding out whether someone has had the infection and is therefore protected. When a recent infection is suspected, the result is always assessed together with IgM, and in pregnant women or people with a weakened immune system it is supplemented with a PCR test, because that detects the virus itself. For people without symptoms and without a pregnancy or immune problem, the result changes little.

What can affect the result?

IgG only develops one to several weeks after infection; shortly after contact, the result can still be negative while there is an infection.
The result says nothing about an infection right now; IgM and a PCR test are needed for that.
With a weakened immune system, antibodies may not be formed, so a negative result does not rule out a past or active infection.
After a blood transfusion or treatment with immunoglobulins, antibodies from donors can temporarily be measured as well.

Who it is for

Who is the test useful for?

Useful for

Useful for pregnant women or women who want to have children who have been in contact with someone with fifth disease or who work with young children, and for people with congenital anemia or a weakened immune system, in whom the infection can be more severe. In people without symptoms and without any of these situations, the result changes little, because most adults have already had the infection and there is no vaccine.

How common is it?

About 61 to 70 in 100 adults in the Netherlands have IgG antibodies against parvovirus B19 and have therefore had the infection. Fifth disease mainly occurs in children of primary school age, with outbreaks in spring. In children, about 5 to 10 in 100 have joint symptoms as well as the rash; in adults, joint symptoms are actually the main feature.

The LCI guideline (RIVM) on parvovirus B19 infection

Drawbacks and risks

A negative result during pregnancy can cause worry, while there is no vaccine and the chance of problems is small even then.
A positive result can wrongly give the impression that there is an infection right now; IgG only says something about the past.

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