What is rheumatoid factor?
Rheumatoid factor is an antibody directed against the tail piece of your own IgG antibodies. That sounds odd, but it is an ordinary reaction of the immune system to lasting stimulation: with a persistent infection, a chronic inflammation and also with getting older, some people make this antibody without anything being wrong with their joints. In rheumatoid arthritis the stimulation is the disease itself, and there rheumatoid factor is present in about seven in ten people. That makes the test sensitive but not specific. A positive rheumatoid factor means the immune system is stimulated, not by what. Five percent of healthy people have it, rising to one in five over seventy; smokers have it more often, and hepatitis C, long-lasting infections, Sjögren's syndrome and lupus produce it too. Anti-CCP is the younger test that solves that problem by being positive almost only in rheumatoid arthritis. Your report shows rheumatoid factor in IU/ml with a limit that differs per lab: one lab calls the result negative below 14 IU/ml, another already below 3.5 IU/ml. A value between those two is therefore called negative at one lab and positive at another. The higher the value above your own lab's limit, the more it says.
Why is rheumatoid factor relevant?
Rheumatoid factor is worth measuring with joint complaints, and then above all together with anti-CCP. With painful, swollen joints that are stiff in the morning and affected on both sides, a positive rheumatoid factor makes rheumatoid arthritis more likely, and positive on both antibodies is the strongest pattern; a high rheumatoid factor also goes with a form of the disease that runs more stubbornly. Because early treatment makes the difference between joints that stay intact and joints that deform, that is the situation in which this number counts. Without joint complaints a positive rheumatoid factor says little. Most people with a positive result do not have rheumatoid arthritis and will not get it; the antibody then belongs to age, to smoking, to a past infection or to nothing in particular. That is why this is not a test for a health check, and why in general practice it is no longer used as a first step when rheumatoid arthritis is suspected: the joints themselves say more than the blood. What you influence yourself is small but real: smoking raises the chance of rheumatoid factor and of rheumatoid arthritis, and healthy gums and a healthy weight lower that chance. That is the same prevention as with anti-CCP.
Rheumatoid factor decision limits
What counts beside the number:
- Your joints: which ones, for how long, on both sides, and how stiff in the morning
- Anti-CCP, which is more specific; both positive is the strongest pattern
- CRP and ESR, which show whether there is inflammation at that moment
- How far the value sits above your own lab's limit, because that limit differs per lab by a factor of four
- Your age, smoking and a recent or lasting infection, the usual explanations without complaints
- Dry eyes and mouth, a rash or other complaints that point at another autoimmune disease
The rows above are limits, not normal values, and they differ per lab by a factor of four: the same value is called negative at one lab and positive at another. So read your result against the limit on your own report, and compare over time at the same lab. In general practice the test is no longer used as a first step when rheumatoid arthritis is suspected, because the diagnosis is made on the joints and not on blood alone.
What Dutch labs actually use
This is the widest gap across these four antibody pages. The limit below which a result is called negative differs by a factor of four between the labs. Unilabs puts it at 14 and Certe runs its band from 0 to 14; Star-shl and Clinical Diagnostics put it at 3.5. A result of 10 is therefore called negative by Unilabs and Certe and sits above the limit at Star-shl and Clinical Diagnostics; Star-shl calls that region positive. The same blood, opposite labels, and each lab is right within its own table. That difference sits in the determination, not in your blood. Star-shl is also the only lab that publishes a middle zone: negative below 3.5, equivocal from 3.5 to 5.0 and positive above 5.0. The other three draw a single line. The unit is shared here: all four report in IU/ml, though Certe writes it as [IU]/mL.
0 – 3.5IU/ml
Between 3.5 and 14 it depends on the lab, because each sets its limit on its own method. Above 14 every lab calls it raised.
From 0 – 3.5 IU/ml no lab calls it raised. Between 3.5 and 14 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | All ages | < 14 IU/mlDecision limit |
| Star-shl2026 | Negative | < 3.5 IU/mlDecision limit |
| Equivocal | 3.5–5.0 IU/mlDecision limit | |
| Positive | > 5.0 IU/mlDecision limit | |
| Certe2026 | All ages | 0–14 IU/mlDecision limit |
| Clinical Diagnostics2026 | All ages | < 3.5 IU/mlDecision limit |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Rheumatoid factor high or low: what it means
A positive rheumatoid factor is, in order of how often it occurs: rheumatoid arthritis in people with joint complaints, an ordinary finding in older people and smokers, a reaction to a lasting or past infection such as hepatitis C, and another autoimmune disease such as Sjögren's syndrome or lupus. The higher the value, the more likely a real cause; a low-positive value in someone without complaints is usually noise. A negative rheumatoid factor is the ordinary outcome, and does not rule rheumatoid arthritis out: three in ten people with the disease do not have it, especially at the start. With persistent complaints it is repeated after a while, together with anti-CCP. What you do about it depends on the context. With complaints and a positive result, seeing a rheumatologist quickly is the step that protects the joints. Without complaints there is nothing to treat and much to gain from not smoking, healthy gums and staying alert to swollen joints. Read rheumatoid factor beside anti-CCP, which is more specific, beside CRP and ESR, which show whether there is inflammation, and beside the joints themselves. Compare over time at the same lab, because the limit differs per lab by a factor of four.
What lowers it
Negative is the ordinary outcome, and does not rule rheumatoid arthritis out.
| Cause | How often |
|---|---|
| Rheumatoid arthritis without rheumatoid factorThree in ten people with the disease do not have the antibody, especially at the start; anti-CCP and the joints themselves are then decisive | Sometimes |
What raises it
Rheumatoid arthritis with complaints; without complaints usually age, smoking or an infection.
| Cause | How often |
|---|---|
| Rheumatoid arthritisPresent in about seven in ten people with the disease; a high value goes with a more stubborn course | Often |
| AgeThe antibody occurs in five percent of healthy people and in one in five over seventy, without anything being wrong with the joints | Often |
| SmokingSmokers make rheumatoid factor and anti-CCP more often, and have a greater chance of rheumatoid arthritis | Sometimes |
| A lasting or past infectionHepatitis C, bacterial heart valve infection and other lasting infections stimulate the immune system into this antibody; it falls again once the infection is gone | Sometimes |
| Other autoimmune diseasesSjögren's syndrome, lupus and some autoimmune liver diseases produce rheumatoid factor without rheumatoid arthritis | Sometimes |
How does a rheumatoid factor blood test work?
- Referral
- Not needed to have the test done, but this is a test for joint complaints and not screening: without complaints a positive result is usually noise.
- Fasting
- Not needed.
- The result
- A single number in IU/ml with your own lab's limit beside it; that limit sits at 14 IU/ml at one lab and at 3.5 IU/ml at another, so compare only with your own report.
- Repeating
- A negative result with persistent joint complaints after a few months, together with anti-CCP. A low-positive result without complaints does not need following.
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is rheumatoid factor?
An antibody directed against the tail piece of your own IgG antibodies. The immune system makes it under lasting stimulation: in rheumatoid arthritis, but also with persistent infections, other autoimmune diseases, in smokers and in some healthy older people. That is why it is sensitive to rheumatoid arthritis but not specific, and why it is always read beside anti-CCP.
What is a normal rheumatoid factor level?
There is no normal value, only a limit, and that differs per lab: one lab calls the result negative below 14 IU/ml, another already below 3.5 IU/ml. Negative is the ordinary outcome. A value between those two limits is therefore called negative at one lab and positive at another; read your result against the limit on your own report.
What does a positive rheumatoid factor mean?
That depends on your joints. With painful, swollen joints that are stiff in the morning, a positive result fits rheumatoid arthritis, certainly together with a positive anti-CCP, and seeing a rheumatologist quickly is the step that protects the joints. Without complaints a positive result usually belongs to age, smoking, a past infection or another autoimmune disease, and the lower the value, the more likely it is noise.
What does a negative rheumatoid factor mean?
In most people: nothing special. With joint complaints a negative result does not rule rheumatoid arthritis out, because three in ten people with the disease do not have the antibody, especially at the start. The diagnosis is then made on the joints themselves, anti-CCP and the inflammation values, and with persistent complaints the test is repeated.
I have no complaints but a positive rheumatoid factor; do I have rheumatoid arthritis?
Probably not. Five percent of healthy people have the antibody, and over seventy one in five; smokers and people after an infection more often. Most people with a positive result without complaints do not get rheumatoid arthritis. What you can do: not smoke, keep healthy gums and a healthy weight, and stay alert to swollen joints or joints stiff in the morning. A low-positive value does not need following.
What is the difference with anti-CCP?
Rheumatoid factor is more sensitive but less specific: it also occurs with infections, other autoimmune diseases and healthy older people. Anti-CCP belongs almost exclusively to rheumatoid arthritis and is often present years before the complaints. Together they say more than either alone: both positive is the strongest pattern, and only rheumatoid factor positive calls for context.
Why does the limit differ so much per lab?
Because the labs work with different assays and have each set their own limit, and those sit a factor of four apart. That sits in the measurement, not in your blood. So compare your result only with the limit on your own report, and have a repeat done at the same lab.
Do I need to fast?
No. Have anti-CCP, CRP and ESR taken in the same draw, because rheumatoid factor is never read alone.
Which tests include rheumatoid factor?
Rheumatoid factor is measured in the Autoimmunity & coeliac module, on top of another draw. It is not orderable yet.
Related biomarkers
Sources
- 1.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
- 2.Unilabs, test catalogue (Dutch): rheumatoid factor IgM. 2026. bepalingenklapper.nl
- 3.Star-shl, test catalogue (Dutch): rheumatoid factor IgM. 2026. star-shl.nl
- 4.Certe, test catalogue (Dutch): rheumatoid factor IgM. 2026. bepalingenwijzer.certe.nl
- 5.Clinical Diagnostics, lab guide (Dutch): IgM-RF (rheumatoid factor). 2026. clinicaldiagnostics.nl
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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Rheumatoid factor is measured in the Autoimmunity & coeliac module, on top of another draw. It is not orderable yet.
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