Rheumatoid factor: what it is, what it tells you and when it’s tested

Rheumatoid factor is an antibody your body makes against its own antibodies. Doctors mostly look for it when they suspect rheumatoid arthritis. But on its own it is not enough for a diagnosis.

When it’s tested

Doctors order it when you have swollen, painful joints, especially in the hands, wrists or feet, with morning stiffness that lasts a long time. Usually together with anti-CCP antibodies: together they say more.

It is also used for some other autoimmune conditions, such as Sjögren’s syndrome.

It is not a test for people who feel well and have no joint pain: a positive result with no symptoms is common and often brings only worry. That is why Rosa does not test it. Instead it looks at high-sensitivity CRP, which flags inflammation, and your blood count.

What it tells you, and what it does not

It is positive in about seven in ten people with rheumatoid arthritis. If it is very high, and symptoms are there, the diagnosis becomes more likely.

But it is also positive in other conditions: other autoimmune diseases, long infections such as hepatitis C, and lung and liver disease. And in some healthy people, more often with age.

A negative rheumatoid factor does not rule out rheumatoid arthritis. There is a form called seronegative, and early in the disease it may not have risen yet.

That is why it is read together with other tests:

Normal rheumatoid factor levels

There is no single value for everyone. Each lab, depending on its method, prints a limit on the report: below it the result is negative, above it positive.

How far above also matters. Rheumatologists separate a low positive, up to three times the lab limit, from a high positive, more than three times. A high positive weighs more in the diagnosis.

With age it turns positive more often, even without disease. You do not need to fast.

If your rheumatoid factor is high or negative

Why rheumatoid factor is high

The most common causes, not in order of seriousness.

What to know before reading it

A few things change the result without changing your health.

When to worry

Talk to your doctor if:

Frequently asked questions

What is a normal rheumatoid factor level? It depends on the lab and the method. Your report prints a limit: below it is negative, above it positive. More than three times the limit is a high positive.

High rheumatoid factor without joint pain: what does it mean? Often nothing serious. It can come from an infection, another condition or simply age. Your doctor decides whether more tests are needed, such as anti-CCP.

Does a positive rheumatoid factor mean rheumatoid arthritis? No. Many people with a positive rheumatoid factor do not have rheumatoid arthritis, and about three in ten people with the disease test negative. The diagnosis comes from an examination, your symptoms and several tests.

Rheumatoid factor or anti-CCP: which is better? They are usually done together. Anti-CCP is more specific: it turns up positive less often in people without the disease. Rheumatoid factor adds information.

Does Rosa test rheumatoid factor? No. Rosa measures high-sensitivity CRP and your blood count, which show whether there is inflammation. If your doctor wants rheumatoid factor, they order it separately.

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