Rheumatoid factor (RF) is a type of antibody that can attack healthy tissues in your body. These types of antibodies are generally known as autoantibodies.
A healthy person’s immune system doesn’t typically produce RF. Because of this, the presence of RF in your blood can indicate that you have an autoimmune condition.
The titer, or amount, of RF is measured using international units per milliliter (IU/mL). The normal range of RF can vary, but it’s typically less than 14 IU/mL.
Sometimes people without any health problems produce a small amount of RF. However, this is rare, only being documented in
Other health issues that can cause higher-than-normal levels of RF include:
- chronic infections
- cirrhosis, which is scarring of the liver
- cryoglobulinemia, which is the presence of abnormal proteins that can block blood flow
- dermatomyositis, which is an inflammatory muscle disease
- mixed connective tissue disease (MCTD)
Some health issues may cause elevated RF levels, but the presence of this antibody alone isn’t used to diagnose these illnesses. These conditions include:
Doctors commonly order this test for people who have symptoms of RA, which include:
- joint pain and stiffness
- warmth and swelling of the joints
- joint stiffness that’s worse in the morning
- reduced appetite
- nodules under the skin
- loss of cartilage or bone
Your doctor may also order tests to diagnose Sjögren’s disease, a condition in which your white blood cells attack the mucous membranes and moisture-secreting glands of your eyes and mouth.
The symptoms of this chronic autoimmune condition are primarily dry mouth and dry eyes. They can also include extreme fatigue, joint pain, and muscle pain. Sjögren’s disease primarily occurs in women and sometimes appears with other autoimmune conditions, including RA.
The RF test is a simple blood test.
During the test, a healthcare professional draws blood from a vein in your arm or the back of your hand. The blood draw only takes a few minutes. For it, the healthcare professional will perform the following steps:
- Clean the skin over your vein.
- Tie an elastic band around your arm so the vein fills quickly with blood.
- Insert a small needle into the vein.
- Collect your blood in a sterile vial attached to the needle.
- Cover the puncture site with gauze and an adhesive bandage to stop any bleeding.
- Send your blood sample to a lab to be tested for RF.
It’ll typically take a few business days to receive your results. When your results are ready, someone from the healthcare facility may contact you to go over them. If you don’t hear back within a few days, follow up with the ordering physician.
You may feel mild to moderate pain during the test.
Complications are rare, but any of the following may occur at the puncture site:
You have a small risk of developing an infection any time your skin is punctured. To avoid this, keep the puncture site clean and dry.
Because vein size varies from person to person, some people may have an easier time with blood draws than others. If it’s difficult for the healthcare professional to access your veins, you may have a slightly higher risk of the minor complications noted above.
Generally speaking, an RF test doesn’t cost that much, between $15 and $26 on average in the United States. However, cost can also depend on where the test is performed and if you received any additional tests at the same time.
Online test kits, which require you to draw your own blood and send the sample off to a laboratory, may cost around $39 to $100, if not more.
If you have health insurance, it’ll likely cover most or all the costs of an in-person test. It’s possible that you may be responsible for paying a small coinsurance or copay. If you have questions about what’s covered, contact your insurance provider prior to your test.
Test results are reported as a titer, which is a measure of the amount of RF antibodies per milliliter of blood. The unit that’s used to report the result is international units per milliliter (IU/mL).
Normal RF levels are typically less than 14 IU/mL. However, this may vary slightly depending on the laboratory performing the test. Some facilities consider RF levels to be normal if they’re less than 20 IU/mL.
If RF levels fall within the normal range, your test result is considered negative. If your RF levels are higher than the normal range, your result is considered positive.
It’s also possible that a positive result may be recorded as either a low positive or a high positive. This is based on
A low-positive result is no more than three times above the upper limit of normal. A high-positive result is over three times the upper limit of normal. So, for example, if we’re using 20 IU/mL as the cutoff for normal RF levels:
|Rheumatoid factor in international units per milliliter (IU/mL)
|Below 20 IU/mL
|20 — >60 IU/mL
|60 IU/mL and above
That said, remember that reference ranges can vary by laboratory, which means the cutoffs for what’s considered a normal RF level may be slightly different. Always refer to the reference ranges listed on your laboratory report when interpreting your test results.
About 80 to 90 percent of people with RA test positive for RF. Additionally, higher levels of RF typically indicate more severe disease and a more challenging outlook. Taking certain disease-modifying agents can lead to a decrease in RF levels.
Additional laboratory tests for RA
- Anticitrullinated protein (anti-CCP) antibody test. Anticitrullinated protein antibody (anti-CCP) antibodies can be detected in about 60 to 70 percent of people with RA. Unlike RF, anti-CCP antibodies are rarely found in people without RA, making them an effective biomarker for RA diagnosis.
- C-reactive protein (CRP) test. This test measures C-reactive protein, which is made by the liver and is associated with inflammation. CRP can be high in inflammatory autoimmune conditions such as RA and lupus. It can also be elevated due to infections or sepsis.
- Erythrocyte sedimentation rate (ESR) test. When inflammation is present, red blood cells can clump together. An erythrocyte sedimentation rate (ESR) test measures the rate that these red blood cells fall to the bottom of a test tube. High ESR can signal inflammation in the body due to autoimmune diseases such as RA and lupus, infections, or some types of cancer.
- Antinuclear antibody (ANA) test. Antinuclear antibodies (ANAs) are also a type of autoantibody found in people with RA. While some people with RA test positive for ANAs, they’re more commonly used in the diagnosis of conditions such as lupus, Sjögren’s disease, and scleroderma.
An RF test requires a sample collected from a simple blood draw and is often used to help diagnose RA. It may also be used to diagnose other health conditions as well, including — but not limited to — Sjögren’s disease, MCTD, and lupus.
Remember that receiving a positive RF test result does not automatically mean you have RA. A combination of other biomarkers is commonly used to help determine an RA diagnosis, such as tests for anti-CCP antibodies, CRP, and ESR.
Your doctor will take into account the results of your RF test, the results of any other tests you’ve had, and, more importantly, your symptoms and clinical examination to determine a diagnosis.