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) by finding and measuring 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 there are inflammatory or autoimmune processes occurring. High levels of RF in your blood indicate that you may have an autoimmune disease like RA or Sjögren's syndrome. However, RF can also be found in a small percentage of healthy people, particularly aging individuals.

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 percent of adults who have RA, if you have signs and symptoms of RA, such as stiffness, swelling, pain, and warmth in your joints, as well as fatigue, fever, and weight loss, this may be one of the first tests your doctor orders. 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 when you're in the early stages of the disease, it takes a variety of blood tests that are used together with an evaluation of your signs and symptoms to diagnose RA. The RF test is usually ordered 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 like the C-reactive protein (CRP) test and/or erythrocyte sedimentation rate (ESR or sed rate), as well as a complete blood count (CBC) to look at your blood cells and an antinuclear antibody (ANA) test to help rule out or diagnose RA.

Sjögren's Syndrome: Your doctor may also order the RF test if you have signs and symptoms of Sjögren's syndrome such as dry mouth, dry eyes, difficulty swallowing, fatigue, not being able to smell or taste as well as you used to, dry skin, increased numbers of cavities, joint swelling and pain, rashes, muscle pain, fever, and a dry cough. RF is commonly seen in people with Sjögren's, so this test can help support a definitive diagnosis.

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 an ANA test and a test to look for antibodies that are specific to Sjögren's syndrome called anti-Ro (SSA) and anti-La (SSB). These two tests are positive in the majority of people with Sjögren's syndrome. You may also have a test to check your immunoglobulins, blood proteins that are often elevated when you have Sjögren's syndrome. Your doctor may also order a CRP test, sed rate, and a CBC to look at your blood cells and possible inflammatory activity. All of these tests together help your doctor make a diagnosis.

The preparation you will need for an RF test depends on what other tests you may be having along with it if any. Your doctor will discuss the tests he or she is 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 the other blood tests mentioned above that you may have 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 blood tests mentioned that you may have with it. If you have different blood tests than these, 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.

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 he or she can take appropriate precautions, such as having you lie down.

Throughout the Test: The actual blood draw normally only takes 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. She'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 begins to get 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 any 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 will be able to go home as soon as you're feeling better.

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 in the area in which your blood was drawn, but this should go away within a few days. If it doesn't 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.

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 at least 1 percent to 5 percent of healthy people (some studies show even higher percentages), particularly older individuals, have a low to moderate amount of RF in their blood for unknown reasons. Additionally, in up to 50 percent of people with RA, both the anti-CCP and RF tests are negative when they first see their doctor for a diagnosis, and up to 20 percent of these people continue to have very little 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.

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. There are other autoimmune diseases that can raise rheumatoid factor levels as well, including:

• Systemic lupus erythematosus
• Scleroderma
• Polymyositis
• Dermatomyositis
• Mixed connective tissue disease
• Mixed cryoglobulinemia syndrome (types II and III)

There are also a number of infections or other medical conditions that can be associated with positive rheumatoid factor test results. Some of them include:

• Bacterial endocarditis
• Tuberculosis
• Syphilis
• Hepatitis
• HIV/AIDS
• Mononucleosis
• Liver cirrhosis and other liver diseases
• Sarcoidosis
• Certain kidney diseases
• Cancer such as multiple myeloma and leukemia
• Lung diseases
• Parasitic infections

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

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

• Positive RF and/or anti-CCP results: If your doctor is looking for rheumatoid arthritis because you have the signs and symptoms and your RF and/or anti-CCP results are positive, especially if your levels are high, this will likely result in a diagnosis of seropositive rheumatoid arthritis. This term reflects that your blood shows high levels of RF and/or anti-CCP antibodies. Other diagnostic criteria include an elevated CRP or sed rate, inflammatory arthritis in three or more joints, symptoms that have persisted for more than six weeks, and that all other diseases with similar symptoms have been ruled out. In general, the higher your RF level, the more severe your disease may be, but this varies case by case.
• Negative RF and anti-CCP results: If you had the RF and anti-CCP tests and both are negative, but your symptoms match up with those associated with rheumatoid arthritis and other diseases have been ruled out, you may be diagnosed with seronegative rheumatoid arthritis, which is less common that 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.

For Sjögren's syndrome, a positive RF test result along with a positive ANA result can help confirm a diagnosis, particularly if your anti-Ro/SSA and anti-La/SSB antibody test is negative. However, both the RF and the ANA have to be positive.

Follow-Up

In the event that 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.

If your doctor is looking for RA and you haven't had the anti-CCP test yet, you'll likely have that next, whether or not your RF test was positive, since the presence of anti-CCP can help diagnose RA. Likewise, if 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're otherwise healthy with no 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.

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

It may take a few days for your rheumatoid factor test results to come back. 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.