What Is a Rheumatoid Factor Test?

A 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.

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

Purpose of Test

The RF test is most often used to help diagnose rheumatoid arthritis (RA) and it's sometimes ordered to support a diagnosis of Sjögren's syndrome, both of which are autoimmune diseases.

Rheumatoid Arthritis

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

• Stiffness
• Swelling
• Pain
• Warmth in your joints
• Fatigue
• Fever
• Weight loss

The 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.

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 RA.

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)
• C-reactive protein (CRP) test
• Erythrocyte sedimentation rate (ESR or sed rate)
• Complete blood count (CBC)
• Antinuclear antibody (ANA) test

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

Juvenile Rheumatoid Arthritis

The RF test is also performed on children suspected of having juvenile RA (JRA) based on a physical examination and symptoms including:

• Joint swelling for at least 6 weeks
• Morning stiffness
• Lessened physical activity
• Decreased motor skills
• Limping or refusal to use a limb
• Fever that comes and goes
• Chronic fatigue or malaise
• Anemia
• Eye inflammation

RF isn't found in JRA as often as it is in adult RA.

All of the tests used to diagnose adult RA may also be ordered for a child with JRA symptoms.

Other possible tests include:

• Comprehensive metabolic panel
• HLA-B27 genetic test
• Synovial fluid analysis
• Blood culture

Sjögren's Syndrome

RF is commonly found in people with Sjögren's, so this test can help support a definitive diagnosis. Your healthcare provider may order the RF test if you have signs and symptoms of Sjögren's syndrome, including:

• Dry mouth
• Dry eyes
• Difficulty swallowing
• Fatigue
• Inability to smell or taste as well as you used to
• Dry skin
• Increased numbers of cavities
• Joint swelling and pain
• Rashes
• Muscle pain
• Fever
• Dry cough

Sjögren's syndrome is another autoimmune disorder that uses a variety of blood tests for diagnosis, along with consideration of your signs and symptoms. Because of this, your healthcare provider will very likely order other blood tests along with the RF test, such as:

• ANA test
• A test to look for Sjögren's syndrome-specific antibodies called anti-Ro (SSA) and anti-La (SSB)
• A test to check your immunoglobulins (blood proteins that are often elevated in Sjögren's syndrome)
• CRP test
• Sed rate
• CBC

All of these tests together help your healthcare provider make a diagnosis.

Risks and Contraindications

A standard blood draw is a low-risk procedure that's perfectly safe for most people.

Before the Test

The preparation you will need for an RF test depends on what, if any, other tests you may be having along with it. Your healthcare provider will discuss the tests you're having, as well as any instructions for them that you may need to follow.

Timing

Blood tests generally only take a few minutes once the technician is ready for you. The RF test can be performed at any time of day.

Location

You might have this test at your doctor's office, a hospital, a clinic, or a laboratory. Your healthcare provider will tell you where to go.

What to Wear

A short-sleeved shirt or a shirt with sleeves that are easy to push up is ideal since the technician will need to access your arm.

Food and Drink

The RF test doesn't require any food, drink, or medication restrictions. If you are also having other blood tests (like cholesterol or glucose levels), you may need to fast before the test. Your healthcare provider will give you specific instructions.

Cost and Health Insurance

An RF test costs an average right around $20, but the cost depends on where you live and what facility performs the test. If you have health insurance, this test should be covered as any diagnostic test would be, though you may need to pay a co-pay and/or co-insurance. Contact your insurer for more details on this.

What to Bring

You should bring your insurance card and a form of identification, as well as a means to pay any co-pay that's required of you.

During the Test

A laboratory technician, a nurse, or a phlebotomist who is specially trained to draw blood will take your blood sample.

Pre-Test

Before the test, you may need to fill out some forms for insurance or consent for the procedure.

If you have a phobia of needles or blood, you need to mention that before the blood draw begins. Be sure to let the technician know ahead of time if you have a history of fainting during medical procedures so they can take appropriate precautions, such as having you lie down.

Throughout the Test

The actual blood draw normally takes just a few minutes. Once you sit down, the technician will ask you to pick which arm you'd like them to use (most people choose their non-dominant side) and have you roll up your sleeve, if needed. They'll find a vein (usually on the inside of your elbow), tie an elastic band around your arm above the vein, and swab the area with alcohol to clean it.

Next, the technician will insert the needle into your vein, which may feel like a sharp prick, sting, or pressure. This should go away very quickly, so let the technician know if it's extremely painful or bothersome and/or if you begin to feel lightheaded or dizzy. Your blood will be collected in a tube. As the tube gets full, the technician will untie the elastic band from around your arm. The needle will be pulled out, which usually doesn't cause any pain, and the area where the needle was placed will be bandaged to prevent further bleeding.

Post-Test

Once your blood has been drawn, you'll be able to leave right away. If you felt faint, you may need a little recovery time, but you'll be able to go home as soon as you're feeling better.

After the Test

You can go about your regular activities and diet as usual once you are finished with the blood draw.

Managing Side Effects

You may experience some pain, swelling, and/or bruising around where your blood was drawn, but this should go away within a few days. If it doesn't go away or it gets worse, let your healthcare provider know. In the meantime, you can use ice packs and take a pain reliever such as Tylenol (acetaminophen) or Advil/Motrin (ibuprofen) as needed.

Interpreting Results

It could take a few days for your rheumatoid factor test results to come back. Your RF test results may come back as either a value or a titer, which indicates the concentration of RF in your blood. What's considered in the normal range can vary a bit between laboratories, but here's a general reference for normal results:

• Value: Less than 15 IU/ml or less than 40 to 60 u/ml (the measurement will depend on the test the lab uses)
• Titer: Less than 1:80

A test is considered positive, high, or elevated if the result is higher than normal. It's considered negative if the result is within the normal range.

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.

Between 5% and 10% of healthy people (or even more according to some studies), particularly older individuals, have a low to moderate amount of RF in their blood for unknown reasons. For up to 50% of people with RA, both the anti-CCP and RF tests are negative the first time, and up to 20% of these people continue to have very low or undetectable amounts of rheumatoid factor or anti-CCP in their blood throughout the course of their disease.

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/SSA and anti-La/SSB 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 you're diagnosed with seronegative RA, your healthcare provider may order the RF and/or anti-CCP tests again at a later point since some people eventually develop elevated levels and become seropositive.

If initial tests were negative and you haven't had the sed rate, CRP test, CBC, and ANA tests yet, your healthcare provider may order these as well. Abnormal results can also help confirm an RA diagnosis.

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.

Rheumatoid Arthritis Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

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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
  

Other Considerations

If you have any questions about your RF test results and what they may mean for you, be sure to ask your healthcare provider. The results can be confusing since they alone don't absolutely confirm or rule out either rheumatoid arthritis or Sjögren's syndrome.

A Word From Verywell

Keep in mind that your diagnosis doesn't hinge on one test. If you do end up having rheumatoid arthritis or Sjögren's syndrome, diagnosing it early can help the success of your treatment.