What Is a Rheumatoid Factor Test?

What to expect when undergoing this test

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

Rheumatoid factor is an autoantibody, a protein made by your immune system that mistakenly attacks your own healthy tissue, usually when inflammatory or autoimmune processes are occurring. High levels of RF in your blood indicate that you may have an autoimmune disease such as RA or Sjögren's syndrome. However, RF can also be found in a small percentage of healthy people, particularly aging individuals. Additionally, not everyone who tests positive for RF has RA.

Purpose of Test

The rheumatoid factor 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 doctor 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, doctors need to look at a variety of blood tests and evaluate your signs and symptoms to diagnose RA. The RF test is usually ordered along with an anti-cyclic citrullinated peptide (anti-CCP) antibody test to look for anti-CCP, which many people with RA also have. 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.

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

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

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

All of the tests listed above for adult RA may be performed on 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 doctor 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, along with consideration of your signs and symptoms, for diagnosis. Because of this, your doctor 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 doctor make a diagnosis.

Risks and Contraindications

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

If you have a phobia of needles or blood, a condition that affects your blood's clotting ability, or other concerns about whether the test is safe for you, be sure to mention that before the blood draw begins.

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 doctor will discuss the tests they're performing, 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, as well as other blood tests commonly ordered at the same time, can be performed at any time of the day.

Location

This test can be performed at your doctor's office, a hospital, a clinic, or a laboratory. Your doctor 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, nor do the other tests you may have with it. If you have different blood tests than those mentioned here, you may need to fast before the test. Your doctor will give you specific instructions.

Cost and Health Insurance

An RF test is relatively inexpensive, averaging 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 may want to bring your insurance card along in case the facility that performs the test doesn't have your insurance information.

During the Test

A laboratory technician, often a nurse or a phlebotomist, a person 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. 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 her 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 to help push the blood down, 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 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 or actually did 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 doctor 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 from laboratory to laboratory, 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.

One reason for this is that 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. Additionally, in 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.

What this means is that 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 results:

If you have symptoms of RA, and your RF and/or anti-CCP results are positive (and especially if they're 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 varies case by case.

Negative RF and anti-CCP results:

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 as noted above.

Negative RF result:

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.

For Juvenile RA:

As with adult RA, doctors 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.

For 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. However, both the RF and the ANA have to be positive.

Follow-Up

If you're diagnosed with seronegative RA, your doctor may order the RF and/or anti-CCP tests again at a later point since, as mentioned above, some people end up eventually developing elevated levels and becoming seropositive.

If initial tests were negative and you haven't had the sed rate, CRP test, CBC, and ANA tests yet, your doctor may order these as well, as 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 doctor may run these tests again at a later time. The RF test isn't used as a screening tool, however, because the majority of healthy people who have elevated RF don't go on to develop RA.

In cases where your doctor 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 doctor will need to start looking at something else in terms of the 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. Some of them include:

However, the RF test is not used to diagnose any of these other autoimmune diseases, infections, or medical conditions.

If you have symptoms but all tests come back negative, your doctor 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, be sure to ask your doctor. 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 this one test. If you do end up having rheumatoid arthritis or Sjögren's syndrome, diagnosing it early can help the success of your treatment.

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Article Sources
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