Rheumatoid Factor (RF) Tests for Rheumatoid Arthritis and More

How the Test Works, Normal Ranges, and What Happens Next

Rheumatoid factor is an autoantibody that is formed in people who have rheumatoid arthritis. It is a protein made by your immune system. 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.

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

This article discusses the purpose of the RF blood test, what to expect, and understanding the results.

Other Diagnostic Results Used to Diagnose RA
 Verywell / Joshua Seong

Purpose of Test

The RF test is most often used to help diagnose rheumatoid arthritis (RA). Sometimes it is 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. Signs and symptoms of RA, may include:

  • 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-CCP antibodies are a more specific marker for rheumatoid arthritis than RF because they rarely occur in diseases other than RA, whereas RF can occur in many conditions.

The RF test isn't used as a screening tool because the majority of healthy people who have elevated RF don't go on to develop RA.

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 six 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:

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
  • Anti-Ro (SSA) and anti-La (SSB)A test: looks for Sjögren's syndrome-specific antibodies
  • Immunoglobulins test: 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 safe for most people.

Before the Test

There are several factors to keep in mind when preparing for the RF test.

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 because it doesn't require that you've been fasting.

Location

You might have this test performed 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 at the elbow.

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 of $20, but it depends on where you live and the facility that performs the test. If you have health insurance, this test should be covered as a diagnostic test, though you may need to pay a co-pay and/or co-insurance. Contact your insurer for more details if needed.

What to Bring

You should bring your insurance card and a form of identification, as well as a payment method in case that's required.

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, tell the healthcare provider before the blood draw begins. Also let the technician know in advance 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 upper arm, and swab the area with alcohol to clean it.

Next, the technician will insert the needle into your vein, which may feel like a brief sharp prick, sting, or pressure. 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, pressure applied to the area where the needle was placed, and bandaged to prevent further bleeding.

After the 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. You can go about your regular activities and diet as usual after the blood draw.

Managing Side Effects

Occasionally people experience some pain, swelling, and/or bruising around the site where 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. The normal or reference range can vary a bit between laboratories, but a general reference for normal results is as follows:

  • Value: Less than 15 IU/ml
  • Titer: Less than 1:80 (1 to 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 rheumatoid arthritis, Sjögren's syndrome, or any other autoimmune disease.

  • Between 5% and 10% of healthy people, particularly older individuals, have a low to moderate amount of RF in their blood for unknown reasons.
  • Up to 50% of people with RA have negative anti-CCP and RF tests the first time.
  • Up to 20% of these people continue to have very low or undetectable amounts of rheumatoid factor or anti-CCP in their blood throughout their disease.

Your RF test result, whether positive or negative, is 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.

A positive RF test result doesn't mean you necessarily have rheumatoid arthritis or Sjögren's syndrome, though the higher your level of RF, the more likely it is that you have one of these, particularly RA.

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. Seronegative RA 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 six 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.

Initial negative tests. If initial tests were negative, your healthcare provider may order:

  • Sed rate test
  • CRP test
  • CBC
  • ANA

If some or all of these tests show abnormal results, it can help confirm an RA diagnosis.

No RA Symptoms: If your RF test and/or anti-CCP test came back positive but you don't have RA symptoms, 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.

Sjögren's syndrome: When your healthcare provider is looking for Sjögren's syndrome, if your RF test, anti-Ro/SSA, anti-La/SSB antibody tests are all negative (and you don't already have an established autoimmune disease), your healthcare provider will 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.

Doctor Discussion Guide Woman

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

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:

If you have symptoms but all tests come back negative, your healthcare provider may start looking into neurological pain conditions, such as:

Other Considerations

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

Summary

Rheumatoid factor is an autoantibody that forms in people who have rheumatoid arthritis. The RF test is often used to help diagnose rheumatoid arthritis (RA). However, test results can sometimes be negative and other criteria are always used, in addition to the RA test, to diagnose RA.

Other health conditions can also cause RF to be elevated. Talk with your healthcare provider if you are experiencing RA symptoms to determine what tests might be needed and to get help interpreting your results.

16 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Rheumatoid Arthritis Support Network. JRA diagnosis: What is the criteria for diagnosis of juvenile RA?

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Additional Reading

By Carol Eustice
Carol Eustice is a writer covering arthritis and chronic illness, who herself has been diagnosed with both rheumatoid arthritis and osteoarthritis.