Blood draw
Rheumatoid Factor
Rheumatoid Factor (RF) for suspected rheumatoid arthritis.
€ 60,00
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Inflammation and immunity · Blood
Rheumatoid factor IgM (IgM-RF)
The IgM type of rheumatoid factor; the form that rheumatologists use together with anti-CCP when rheumatism is suspected.
At a glance
- Measured in blood
- In 1 test panel
- No special preparation
Explanation
Rheumatoid factor IgM (IgM-RF): what is measured?
Rheumatoid factors are autoantibodies against the body's own immune protein IgG. By far most rheumatoid factor is of the IgM type, and this test measures that type specifically. In the Dutch guideline on rheumatoid arthritis, IgM rheumatoid factor is the test used together with anti-CCP when assessing joint symptoms. A raised value belongs to an inflammatory process, but is not specific to one disease.
What can it detect?
- Rheumatoid arthritis (RA), together with anti-CCP
- Sjögren's syndrome (chronic inflammation of the tear and salivary glands)
- Long-lasting infections and other inflammatory diseases in which rheumatoid factor develops as a side effect
Result
What does the result mean?
Rheumatoid factor IgM (IgM-RF) too high
A raised IgM rheumatoid factor makes rheumatoid arthritis more likely if there is also joint inflammation, especially in combination with a positive anti-CCP. According to the Dutch guideline, the combination of both antibodies is most strongly linked to the development of joint inflammation in people who already have joint pain. Without joint symptoms, a raised value says little: up to 5 in 100 healthy people have rheumatoid factor and/or anti-CCP. Long-lasting infections, other inflammatory diseases and older age also give a raised value without rheumatism.
Rheumatoid factor IgM (IgM-RF) too low
A low or undetectable IgM rheumatoid factor is the normal result. This does not rule out rheumatoid arthritis: about 1 in 5 people with RA have no detectable rheumatoid factor, and some of them do have anti-CCP. With inflamed joints, the symptoms and the physical examination remain decisive.
After an abnormal result
With joint inflammation, the GP usually refers you to a rheumatologist, whatever the result. The rheumatologist assesses rheumatoid factor and anti-CCP together with the examination of the joints. A raised value without symptoms usually does not lead to further tests.
Reliability
How reliable is the test?
IgM rheumatoid factor is more sensitive than specific: it finds many people with RA, but is also often positive without rheumatism. The Dutch guideline on rheumatoid arthritis advises measuring anti-CCP and rheumatoid factor together in people with joint inflammation or clear joint pain who are seen by a rheumatologist, and takes false-positive results into account, especially from rheumatoid factor. According to the Dutch Society for Clinical Chemistry (NVKC), the test is almost never needed in primary care, because a strong clinical suspicion is already enough reason to refer.
What can affect the result?
- A raised IgM rheumatoid factor also occurs in healthy people, more often at older ages.
- Long-lasting infections, sarcoidosis and diseases of the lungs, liver or kidneys can raise the value.
- Measurement methods and cut-off values differ between laboratories; results are not interchangeable between labs.
- The value is not suitable for monitoring disease activity during treatment.
Who it is for
Who is the test useful for?
Useful for
Useful with inflamed joints or with joint pain where a doctor is thinking of rheumatoid arthritis, together with anti-CCP. In people without joint symptoms, the test is pointless according to the Dutch Society for Clinical Chemistry (NVKC): the chance that a positive result means rheumatism is then small. A separate IgM test alongside a standard rheumatoid factor adds little information for most people.
How common is it?
Rheumatoid arthritis affects about 0.5 to 1 in 100 people; each year about 3 in 10,000 people are diagnosed with it. Sjögren's syndrome is rarer. A raised rheumatoid factor is more common than these diseases: up to 5 in 100 healthy people have rheumatoid factor and/or anti-CCP, and in older people a positive result without disease is found more often.
NVKC Zinnige Diagnostiek and FMS guideline on rheumatoid arthritis (NVR)
Drawbacks and risks
- A raised IgM rheumatoid factor without joint inflammation is often false positive and can lead to unnecessary worry or referral.
- A normal result does not rule out rheumatoid arthritis.
Get tested
Rheumatoid factor IgM (IgM-RF): test panels
Rheumatoid factor IgM (IgM-RF) 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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