Blood draw · 2 analyses
Rubella (German measles) IgG and IgM
Measures IgG and IgM antibodies against rubella: whether you are protected and whether there are signs of a recent infection. For symptoms or after contact.
€ 51,00
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Other analyses · Blood
Rubella IgM
Antibodies that may point to a recent rubella infection; only interpretable together with IgG and symptoms.
At a glance
- Measured in blood
- In 1 test panel
- Check the preparation
Explanation
Rubella IgM: what is measured?
In an infection with the rubella virus (German measles), the immune system first makes IgM antibodies. According to the LCI guideline (RIVM), these appear about 4 days after the rash starts and are usually detectable for 4 to 12 weeks, sometimes for a year or longer, also after a vaccination. IgG appears almost at the same time and stays. This test measures IgM and is used when a recent infection is suspected, for example in a pregnant woman who has been in contact with someone with rubella.
What can it detect?
- Possible recent rubella infection (together with IgG and symptoms)
- Possible recent infection in a pregnant woman after contact with someone with rubella
Result
What does the result mean?
Positive result
A positive IgM may fit a recent rubella infection, but does not prove it. According to the LCI guideline (RIVM), falsely positive results occur, among others with a parvovirus B19 infection (fifth disease), with glandular fever (Pfeiffer's disease) and with rheumatoid factor in the blood; IgM can also remain detectable long after an infection or vaccination. Because rubella is rare in the Netherlands, a positive IgM in someone without matching symptoms or contact is often not the result of a new infection. With a true infection in the first half of pregnancy, the unborn child runs a high risk of birth defects, such as defects of the heart, eyes and hearing; after week 16, hardly any defects are seen.
Negative result
A negative IgM makes a recent rubella infection less likely. Together with a positive IgG, this fits protection or an infection from longer ago; together with a negative IgG, it means that you are probably not protected. IgM is only reliable from about 4 days after the rash starts; after a contact, the doctor therefore follows the antibodies until at least 3 weeks later. In a second infection in someone who was already protected, IgM usually cannot be detected.
After an abnormal result
With a positive IgM, the GP or midwife has the result confirmed with a second blood draw after 10 to 14 days, another IgM test or a PCR on a throat swab; a pregnant woman is referred to the gynecologist for an explanation of the risks for the child. Rubella is notifiable (group B2): the doctor and laboratory report an infection that meets the notification criteria, including a positive IgM with matching symptoms, within 1 working day to the GGD (municipal public health service), which checks whether there are unprotected pregnant women nearby.
Reliability
How reliable is the test?
According to the LCI guideline (RIVM) on rubella, a positive IgM together with symptoms and medical history makes the diagnosis likely, but a falsely positive result must be taken into account. Especially with a possible infection during pregnancy, confirmation is needed with another IgM test, a PCR on a throat swab or newly drawn blood, before any decision on intervention is made. The most specific confirmation is a clear rise in antibodies between two blood draws at least 10 to 14 days apart.
What can affect the result?
- IgM is only reliable from about 4 days after the rash starts; drawing blood earlier can give a falsely negative result.
- Other infections, such as parvovirus B19 and glandular fever (Pfeiffer's disease), and rheumatoid factor in the blood can give a falsely positive IgM.
- IgM can remain detectable for more than a year after an infection or vaccination.
- In a reinfection in someone who was already protected, IgM is usually not detectable, or only briefly.
Preparation
- Do not have your blood taken earlier than 4 days after the rash started; before that, IgM is often not yet measurable.
Who it is for
Who is the test useful for?
Useful for
Useful with symptoms that may point to rubella, such as spots that start on the face and painful, swollen glands behind the ears or in the neck, and especially in a pregnant woman who is not (certainly) protected and has been in contact with someone with rubella. Drawing blood only makes sense from about 4 days after the rash starts; shortly after a contact, a PCR on a throat swab says more. Without symptoms or contact, this test is not useful, because a positive result is then usually falsely positive; IgG is the test for protection.
How common is it?
Rubella hardly occurs in the Netherlands anymore: usually fewer than 5 infections per year, with an occasional outbreak among unvaccinated groups. About half of the infections cause no symptoms. With a first infection in the first trimester of pregnancy, the unborn child becomes infected in 75 to 100 percent of cases; this risk decreases later in pregnancy.
RIVM; LCI guideline Rubella
Drawbacks and risks
- A falsely positive IgM can cause a lot of worry and extra testing, especially during pregnancy.
- Drawing blood too soon after symptoms or contact can wrongly reassure you.
Get tested
Rubella IgM: test panels
Rubella IgM is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.
Evidence
Sources
This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.
More about risks and resultsMore explanations
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