Rheumatoid Factor (RF)

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  • Also Known As:
  • RF Blood Test
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A rheumatoid factor (RF) test detects rheumatoid factor in a patient’s blood. Rheumatoid factor is an autoantibody produced by the immune system. While normal antibodies attack pathogens like bacteria and viruses, autoantibodies such as RF mistakenly attack the body’s healthy cells and tissues.

Testing for rheumatoid factor is most often used in conjunction with other laboratory and imaging tests to diagnose rheumatoid arthritis or Sjögren syndrome. An RF test may also be helpful in distinguishing rheumatoid arthritis from other autoimmune disorders.

About the Test

Purpose of the test

The purpose of testing for rheumatoid factor is to determine if a patient has RF in their blood. While some healthy people have detectable RF, a positive result on an RF test can also indicate an underlying health condition and may warrant additional diagnostic testing in patients with other signs or symptoms of an autoimmune disorder. An RF test can help doctors diagnose autoimmune disorders and estimate disease severity:

  • Diagnosing autoimmune disorders: Diagnostic testing may be appropriate for patients with symptoms of rheumatoid arthritis, Sjögren’s syndrome, or another autoimmune disorder. For example, a patient’s doctor may recommend a test for rheumatoid factor if a patient is experiencing pain and inflammation in multiple joints that isn’t due to another condition.
  • Estimating disease severity: Rheumatoid factor testing can also provide doctors with information about the severity of rheumatoid arthritis. Patients with higher levels of RF are more likely to have severe rheumatoid arthritis, as well as disease that affects parts of the body outside of the joints, such as the lungs and blood vessels.

Although treatment for rheumatoid arthritis may lower the amount of rheumatoid factor in the blood, repeated testing for RF is not typically used to monitor patients during treatment for rheumatoid arthritis.

What does the test measure?

Rheumatoid factor testing measures the amount of the rheumatoid factor in the blood. There are several ways to measure RF, one of which is an antibody titer test. Antibody titer tests detect how much of a specific type of antibody is present in the blood.

The development of RF and how it affects the body is not well understood. Researchers believe that rheumatoid factors may be the result of the body’s response to pathogens, like bacteria or viruses, and other triggers that confuse the immune system.

When should I get rheumatoid factor testing?

A doctor may recommend a rheumatoid factor test if a patient is experiencing symptoms of rheumatoid arthritis. Symptoms of rheumatoid arthritis include:

  • Joint symptoms, including pain, swelling
  • Morning stiffness for 30 minutes or longer
  • Tiredness or fatigue
  • Intermittent fever
  • Appetite loss
  • Weight loss
  • Weakness
  • Dry eyes and mouth
  • Firm lumps beneath the skin

Rheumatoid factor testing is not used as a screening test for rheumatoid arthritis in patients without symptoms. Most patients who test positive for RF but don’t have symptoms never go on to develop rheumatoid arthritis.

Doctors may also order an RF test while testing for other health conditions. Other conditions in which RF testing may be used include:

  • Sjögren’s syndrome
  • Lupus
  • Juvenile arthritis
  • Scleroderma
  • Certain infections, including mononucleosis or tuberculosis
  • Certain types of cancer, including leukemia
  • Hepatitis C

Finding a Rheumatoid Factor Test

 

How to get tested

Rheumatoid factor testing is ordered by a doctor. A patient’s doctor may suggest a rheumatoid factor test alone, but usually this test is used along with other tests to evaluate a patient for an autoimmune disorder. RF testing requires a blood sample that is normally drawn in a doctor’s office, hospital, or laboratory.

Can I take the test at home?

While not common, at-home testing for rheumatoid factor is available and can detect the level of RF in the blood. Taking an at-home RF test involves pricking a finger and collecting a small sample of blood. The blood sample is then sent to a laboratory for analysis and results are returned to the patient via the company’s website or smartphone application.

At-home testing kits may combine an RF test with a test for cyclic citrullinated peptide (CCP) antibodies. While both RF and CCP antibodies are biomarkers that may indicate a person’s likelihood of having rheumatoid arthritis, neither of these tests are able to definitively diagnose the condition. Doctors use the results of these tests in combination with other factors to diagnose rheumatoid arthritis and other autoimmune disorders.

How much does the test cost?

The cost of rheumatoid factor testing depends on whether or not a patient’s health insurance covers this type of testing. The cost of testing can also vary based on where the test is conducted and whether RF testing is combined with other tests.

For patients with health insurance, fees for the blood draw, laboratory analysis, and office visits may be included in the cost of RF testing. A patient’s health insurance often covers most or all of these costs when the test is prescribed by a doctor. It’s important for patients to talk to their health insurance company to understand deductibles or copays that may be required.

At-home tests may not be covered by a patient’s health insurance and cost around $100.

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Taking a Rheumatoid Factor Test

 

A rheumatoid factor test is performed on a blood sample that is typically taken from a vein in a patient’s arm. The sample of blood can be drawn in a doctor’s office, health clinic, or laboratory.

For an at-home RF test, a blood sample is obtained by pricking a finger and collecting the sample as instructed in a test kit.

Before the test

Generally, taking a rheumatoid factor test requires no special preparations. Patients may still find it helpful to talk to their doctor before the test about any medications or supplements that they are taking, as well as any questions or concerns about the RF test.

Before taking an at-home RF test, patients should read the instructions provided in the test kit carefully and consult the testing company or their doctor if they need additional guidance.

During the test

To obtain the necessary blood sample for a rheumatoid factor test, a sample of blood is drawn from a vein in the patient’s arm, usually inside of the elbow or on the back of the hand.

The health care provider conducting the blood draw will first locate an appropriate vein. Next, the provider will place an elastic band a few inches above the vein to increase blood flow. The skin is then cleaned and a needle is inserted into the vein. Blood is collected in a test tube or vial before the elastic band is removed and the needle is withdrawn.

This process typically takes less than five minutes. Patients may feel a stinging sensation when the needle is inserted and removed. Many patients also feel some throbbing at the site after the blood is drawn.

For an at-home RF test, all necessary materials for sample collection are provided in the test kit. Patients begin testing by cleaning their fingertip and pricking it with a provided lancet or needle to obtain a drop of blood. The patient then collects a few drops of blood in a collection device or test tube. The collection device is then packaged and sent to a lab by mail.

After the test

After completing a blood draw, a health care provider will apply a bandage and pressure to stop any bleeding at the site of the blood draw. There is little risk in having a blood draw. Some patients experience temporary pain or minor bruising. There are no restrictions on activities after RF testing.

For an at-home RF test, patients can apply a bandage to their fingertip to stop any bleeding after collecting the blood sample.

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Rheumatoid Factor Test Results

 

Receiving test results

Test results are normally available within a few business days of taking a rheumatoid factor test. Results may be shared with a patient over the phone, by mail, or electronically. In some cases, doctors may wait to share the results of RF testing until other testing is completed.

Results from at-home RF testing may take additional time as the test sample must first be mailed to the appropriate laboratory. Test reports may be available through the company’s website or a smartphone app. Some at-home testing companies connect patients to a health professional for support in understanding the test result.

Interpreting test results

After an RF test is completed, test results are reported as either positive or negative. A numerical or titer value may be provided to indicate the level of RF detected in the blood. Negative results may also be called normal, while positive results may be called abnormal.

Reference ranges for this test vary by laboratory and by the type of RF test performed in the analysis. In interpreting test results, it’s important to use the reference ranges provided by an individual laboratory.

Because rheumatoid factor testing is rarely used alone, results of an RF test should be interpreted with caution. A negative test result indicates that little to no RF was found in the blood, but this does not always rule out an underlying health issue. Up to 20% of people with rheumatoid arthritis may have a negative RF test result, and their result may change over time.

Testing positive for rheumatoid factor may indicate an underlying health condition but is insufficient to diagnose a condition on its own. Around 5 to 10% 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 that a patient has an autoimmune disorder. In order to diagnose the cause of a patient’s 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.

Diagnosing autoimmune disorders can be complex, so it’s important to work with a doctor when interpreting test results. Patients may also benefit from consulting with a rheumatologist. Rheumatologists are doctors that specialize in diagnosing and treating autoimmune disorders and other conditions of the joints, muscles, and bones. A rheumatologist can help patients understand their test results, as well as answer questions about the process of diagnosing autoimmune disorders.

Are test results accurate?

Rheumatoid factor testing is an important aspect of diagnosing certain health conditions and is generally regarded as accurate. Like any medical test though, RF testing is not perfect. Issues may arise in the processing or analysis of test samples and laboratories take special precautions to reduce the incidence of errors.

In order to reduce the likelihood of false positive results, in which a person tests positive for RF but doesn’t have an underlying health condition, doctors may restrict RF testing to those with a high probability of having rheumatoid arthritis. In patients who aren’t likely to have rheumatoid arthritis based on their history and physical exam, the value of RF is poor, and false positives are more likely to occur.

Do I need follow-up tests?

When evaluating patients for rheumatoid arthritis, RF test results are combined with other tests and the findings of a physical exam. Together, these factors help doctors determine the need for follow-up testing.

In patients with a high probability of having rheumatoid arthritis, positive RF test results may be followed up by testing for CCP antibodies, erythrocyte sedimentation rate (ESR), and c-reactive protein (CRP) to confirm a diagnosis of rheumatoid arthritis. If a CCP antibody test is negative, doctors may recommend antinuclear antibody (ANA) testing, testing for hepatitis B and hepatitis C, a synovial fluid analysis, as well as imaging tests.

If a doctor rules out rheumatoid arthritis in a patient with a positive RF test result, they may perform testing for other disorders that are associated with having detectable RF in the blood. These disorders include other types of arthritis, chronic infections, lung disorders, inflammatory bowel disease, and cancer.

Questions for your doctor about test results

A patient’s doctor can help to address questions about rheumatoid factor testing and test results. Some questions that may be helpful to review with a doctor include:

  • How does my test result help me understand the cause of my symptoms?
  • Based on my test result, what is the likelihood that I have rheumatoid arthritis or another autoimmune disorder?
  • Do I need any follow-up tests based on my test result?

Related Tests

 

How is a rheumatoid factor test different from a cyclic citrullinated peptide antibody test?

Rheumatoid factor and CCP are both autoantibodies produced by the immune system that cause disease by mistakenly attacking the body’s healthy tissue. While both types of autoantibodies are tested if doctors suspect rheumatoid arthritis, testing for CCP is considered more specific than testing for RF and can offer more definitive evidence for a diagnosis of rheumatoid arthritis.

Other related tests

Sources and Resources

The following resources provide additional information about rheumatoid arthritis and rheumatoid factor testing:

Sources

A.D.A.M. Medical Encyclopedia. Autoimmune disorders. Updated April 8, 2019. Accessed May 12, 2021. https://medlineplus.gov/ency/article/000816.htm

A.D.A.M. Medical Encyclopedia. Rheumatoid factor (RF). Updated April 8, 2019. Accessed May 12, 2021. https://medlineplus.gov/ency/article/003548.htm

A.D.A.M. Medical Encyclopedia. Venipuncture. Updated April 26, 2019. Accessed May 12, 2021. https://medlineplus.gov/ency/article/003423.htm

A.D.A.M. Medical Encyclopedia. Antibody titer blood test. Updated May 2, 2020. Accessed May 12, 2021. https://medlineplus.gov/ency/article/003333.htm

A.D.A.M. Medical Encyclopedia. Antibody. Updated August 13, 2020. Accessed May 12, 2021. https://medlineplus.gov/ency/article/002223.htm

American College of Rheumatology. What is a rheumatologist? Updated June 2018. Accessed May 12, 2021. https://www.rheumatology.org/I-Am-A/Patient-Caregiver/Health-Care-Team/What-is-a-Rheumatologist

American College of Rheumatology. Rheumatoid arthritis. Updated March 2019. Accessed May 12, 2021. https://www.rheumatology.org/I-Am-A/Patient-Caregiver/Diseases-Conditions/Rheumatoid-Arthritis

Arthritis Foundation. Rheumatoid arthritis: Causes, symptoms, treatments and more. Date unknown. Accessed May 12, 2021. https://www.arthritis.org/diseases/rheumatoid-arthritis

ARUP Consult. Rheumatoid arthritis. Updated October 2020. Accessed May 12, 2021. https://arupconsult.com/content/rheumatoid-arthritis

Baer AN. Diagnosis and classification of Sjögren’s syndrome. In: Fox R, ed. UpToDate. Updated April 29, 2021. Accessed May 12, 2021. https://www.uptodate.com/contents/diagnosis-and-classification-of-sjogrens-syndrome

Centers for Disease Control and Prevention. Rheumatoid arthritis (RA). Updated July 27, 2020. Accessed May 12, 2021. https://www.cdc.gov/arthritis/basics/rheumatoid-arthritis.html

Firestein GS, Guma M. Pathogenesis of rheumatoid arthritis. In: St Clair EW, ed. UpToDate. Updated February 3, 2020. Accessed May 12, 2021. https://www.uptodate.com/contents/pathogenesis-of-rheumatoid-arthritis

MedlinePlus: National Library of Medicine. Rheumatoid arthritis. Published May 2, 2018. Accessed May 12, 2021. https://medlineplus.gov/rheumatoidarthritis.html

MedlinePlus: National Library of Medicine. CCP antibody test. Updated July 30, 2020. Accessed May 12, 2021. https://medlineplus.gov/lab-tests/ccp-antibody-test/

MedlinePlus: National Library of Medicine. Rheumatoid factor (RF) test. Updated December 3, 2020. Accessed May 12, 2021. https://medlineplus.gov/lab-tests/rheumatoid-factor-rf-test/

MedlinePlus: National Library of Medicine. What you need to know about blood testing. Updated March 9, 2021. Accessed May 12, 2021. https://medlineplus.gov/lab-tests/what-you-need-to-know-about-blood-testing/

National Institute of Arthritis and Musculoskeletal and Skin Diseases. Rheumatoid arthritis. Updated September 2019. Accessed May 12, 2021. https://www.niams.nih.gov/health-topics/rheumatoid-arthritis

Schmerling RH. Lab interpretation: Positive rheumatoid factor (RF). In: O’Dell J, ed. UpToDate. Updated March 26, 2020. Accessed May 12, 2021. https://www.uptodate.com/contents/positive-rheumatoid-factor-rf

Shmerling RH. Rheumatoid factor: Biology and utility of measurement. In: Wener MH, ed. UpToDate. Updated April 8, 2021. Accessed May 12, 2021. https://www.uptodate.com/contents/rheumatoid-factor-biology-and-utility-of-measurement

Taylor PC, Deleuran B. Biologic markers in the diagnosis and assessment of rheumatoid arthritis. In: O’Dell J, ed. UpToDate. Updated December 23, 2020. Accessed May 12, 2021. https://www.uptodate.com/contents/biologic-markers-in-the-diagnosis-and-assessment-of-rheumatoid-arthritis

Venables PJW, Baker JF. Diagnosis and differential diagnosis of rheumatoid arthritis. In: O’Dell J, ed. UpToDate. Updated March 15, 2021. Accessed May 12, 2021. https://www.uptodate.com/contents/diagnosis-and-differential-diagnosis-of-rheumatoid-arthritis

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