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Immune System Rheumatoid Arthritis (RA)

Rheumatoid factor (RF)

Optimal Result: 0 - 14 IU/ml.

What is the Rheumatoid factor (RF) test?

The rheumatoid factor (RF) test is a blood test that's often used to help diagnose rheumatoid arthritis (RA). The test measures the amount of RF in your blood.

What is the Rheumatoid factor?

The rheumatoid factor (RF) is an autoantibody that is formed in people who have rheumatoid arthritis. It is a protein made by your immune system. High levels of RF in your blood indicate that you may have an autoimmune disease such as RA or Sjögren's syndrome. However, not everyone who tests positive for RF has RA.

RF can also be found in a small percentage of healthy people, particularly aging individuals.

Why would my doctor order the Rheumatoid factor (RF) test?

Since RF is present in up to 80% of adults who have rheumatoid arthritis (RA), this may be one of the first tests your healthcare provider orders if you have signs and symptoms of rheumatoid arthritis (RA), such as:

→ Stiffness

→ Swelling

→ Pain

→ Warmth in your joints

→ Fatigue

→ Fever

→ Weight loss

The Rheumatoid factor (RF) test can also help distinguish RA from other types of arthritis like osteoarthritis or psoriatic arthritis and may rule out other conditions with similar symptoms.

What other blood test markers need to be looked at for a rheumatoid arthritis diagnosis?

Because rheumatoid arthritis can be tricky to diagnose in the early stages, healthcare providers need to look at a variety of blood tests and evaluate your signs and symptoms to diagnose rheumatoid arthritis.

You may also have blood tests at the same time that can detect inflammation in your body, such as the:

→ Anti-cyclic citrullinated peptide (anti-CCP)

Anti-CCP antibodies are actually a more specific marker for rheumatoid arthritis than Rheumatoid factor (RF), because they rarely occur in diseases other than RA, whereas RF can occur in a large number of conditions.

→ C-reactive protein (CRP) test

→ Erythrocyte sedimentation rate (ESR or sed rate)

→ Complete blood count (CBC)

→ Antinuclear antibody (ANA) test

A negative (normal) result means that you have little or no rheumatoid factor in your blood. But that doesn't rule out rheumatoid arthritis or another health problem. Many people with rheumatoid arthritis have little or no rheumatoid factor. If you have symptoms of rheumatoid arthritis, but your RF test results are normal, your provider may order more tests to make a diagnosis.

References:

Tiwari V, Jandu JS, Bergman MJ. Rheumatoid Factor. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532898/

American College of Rheumatology. Rheumatoid Arthritis - https://www.rheumatology.org/I-Am-A/Patient-Caregiver/Diseases-Conditions/Rheumatoid-Arthritis

Arthritis Foundation. Rheumatoid Arthritis: Causes, Symptoms, Treatments and More - https://www.arthritis.org/diseases/rheumatoid-arthritis

Centers for Disease Control and Prevention. Rheumatoid Arthritis (RA) - https://www.cdc.gov/arthritis/basics/rheumatoid-arthritis.html

MedlinePlus: National Library of Medicine. CCP Antibody Test - https://medlineplus.gov/lab-tests/ccp-antibody-test/

Taylor PC, Deleuran B. Biologic Markers in the Diagnosis and Assessment of Rheumatoid Arthritis. In: O’Dell J, ed. UpToDate - https://www.uptodate.com/contents/biologic-markers-in-the-diagnosis-and-assessment-of-rheumatoid-arthritis

Shapiro SC. Biomarkers in Rheumatoid Arthritis. Cureus. 2021 May 16;13(5):e15063. doi: 10.7759/cureus.15063. PMID: 34141507; PMCID: PMC8205440.

Referenced links:

https://www.testing.com/tests/rheumatoid-factor-rf/

What does it mean if your Rheumatoid factor (RF) result is too high?

An elevated rheumatoid factor test result shows that you have a high level of rheumatoid factor in your blood. A higher level of rheumatoid factor in your blood is closely linked with autoimmune diseases, especially rheumatoid arthritis.

But a number of other diseases and conditions can raise rheumatoid factor levels, including:

→ Cancer

→ Chronic infections, such as viral hepatitis B and C

→ Inflammatory lung diseases, such as sarcoidosis

→ Mixed connective tissue disease

→ Sjogren syndrome

→ Systemic lupus erythematosus

Other factors that can cause increased RF:

Some factors that may increase the risk of RA include age (adults in 60s), gender (females are two to three times more likely to have RA), smoking, women who have not given birth, children of mothers who smoked, and obesity. 

Symptoms of rheumatoid arthritis may include:

→ Joint pain

→ Tenderness, swelling, and warmth of the joint

→ Joint stiffness that lasts longer than 30 minutes

→ Fatigue

→ Occasional low fevers

→ Loss of appetite

Not enough to diagnose:

An RF test alone cannot diagnose any conditions. To make a diagnosis, your provider will look at the results of other tests along with your symptoms and medical history.

Diagnosing autoimmune disorders can be complex. It’s important to work with a doctor or consult with a rheumatologist, a doctor specializing in diagnosing and treating autoimmune disorders and other conditions of the joints, muscles, and bones. A rheumatologist can help you understand your results, as well as answer questions about the process of diagnosing autoimmune disorders.

Estimating disease severity:

RF testing can also provide doctors with information about the severity of RA. If you have higher levels of RF, you are more likely to have severe RA, a more aggressive disease causing erosion of joints, development of rheumatoid nodules, and damaging inflammation of the blood vessels. RF can also affect parts of the body outside of the joints, such as the lungs, eyes, and heart.

Although treatment for RA may lower the amount of RF in the blood, repeated testing for RF is not typically used to monitor you if receiving treatment for RA.

Interpreting test results:

Testing positive for RF may indicate an underlying health condition but is insufficient to diagnose it on its own. Around 4% of healthy people have RF detected in their blood. Positive results may also be related to an underlying autoimmune disorder, certain infections, and some types of cancer.

While high levels alone cannot diagnose any condition, research suggests that the higher the amount of RF in the blood, the greater the likelihood you have an autoimmune disorder.

To diagnose the cause of your symptoms, doctors often combine RF testing with a physical exam, imaging tests, and laboratory tests such as CCP antibody testing, antinuclear antibody (ANA) testing, and a synovial fluid analysis. Up to 30% of RA patients may be negative for RF but often positive for antiCCP, an abnormality that may precede overt symptoms of RA.

Keep in mind that this test is never used by itself to definitively diagnose someone with rheumatoid arthritis, Sjögren's syndrome, or any other autoimmune disease. Your RF test results, whether positive or negative, are just one piece of the diagnostic puzzle.

If your tests for anti-CCP and RF both come back negative but you have ongoing symptoms of RA with no other cause or explanation, you may be in the early stages and could receive a diagnosis anyway.

Here's a look at more specific test results regarding rheumatoid arthritis:

Positive RF and/or Anti-CCP:

If you have symptoms of RA, and your RF and/or anti-CCP results are high, the likely result is a diagnosis of seropositive rheumatoid arthritis.

Other diagnostic criteria for seropositive RA include:

→ Elevated CRP or sed rate

→ Inflammatory arthritis in three or more joints

→ Symptoms that have persisted for more than six weeks

→ All other diseases with similar symptoms have been ruled out

In general, the higher your RF level, the more severe your disease is likely to be, but this is not a rule.

Negative RF and Anti-CCP:

If you had negative RF and anti-CCP tests but you have symptoms consistent with rheumatoid arthritis and other possible diseases have been ruled out, the likely result is a diagnosis of seronegative rheumatoid arthritis, which is less common than seropositive RA.

This means that you don't have the RF and anti-CCP antibodies in your blood, but you meet the other diagnostic criteria.

Negative RF:

If you have signs and symptoms of RA and you had a negative RF test but no other tests at the same time, the next likely step is an anti-CCP test. If it's positive, the likely diagnosis is seropositive RA, provided you meet the rest of the diagnostic criteria.

Juvenile RA:

As with adult RA, healthcare providers look at the total picture, including physical symptoms and a variety of test results. JRA has seven distinct subtypes, each with its own diagnostic criteria. RF is positive in some and negative in others.

Sjögren's Syndrome:

If you have negative anti-Ro/SS-A and anti-La/SS-B antibody tests but a positive RF test and a positive ANA result, the likely result is a diagnosis of Sjögren's syndrome.

Follow up:

If your RF test and/or anti-CCP test came back positive but you don't have RA symptoms, you're not necessarily in the clear. It's possible that you may develop RA over time. This is more likely if your levels are high and substantially more likely when both tests are positive, in which case, your healthcare provider may run these tests again at a later time.

In cases where your healthcare provider is looking for Sjögren's syndrome, if your RF test and anti-Ro/SSA and anti-La/SSB antibody tests are all negative and you don't already have an established autoimmune disease, your healthcare provider will need to consider another cause of your symptoms.

Other autoimmune diseases that can raise rheumatoid-factor levels include:

→ Systemic lupus erythematosus

→ Scleroderma

→ Polymyositis

→ Dermatomyositis

→ Mixed connective tissue disease

→ Mixed cryoglobulinemia syndrome (types II and III)

A number of infections or other medical conditions can be associated with positive rheumatoid factor test results, too. However, the RF test is not used to diagnose any of these other autoimmune diseases, infections, or medical conditions.

Some of them include:

→ Bacterial endocarditis

→ Tuberculosis

→ Syphilis

→ Hepatitis

→ HIV/AIDS

→ Mononucleosis

→ Liver cirrhosis and other liver diseases

→ Sarcoidosis

→ Certain kidney diseases

→ Cancers such as multiple myeloma and leukemia

→ Lung diseases

→ Parasitic infections

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