Rheumatoid Factor (RF) Test: Purpose, Results, Levels
A rheumatoid factor (RF) test detects rheumatoid factor, a type of antibody (proteins that fight off harmful substances) in your blood. RF antibodies sometimes attack healthy cells and tissues, leading to autoimmune conditions.
Rheumatoid factors are commonly used to diagnose rheumatoid arthritis but can also detect other conditions, such as Sjögren syndrome, lupus, hepatitis C, tuberculosis, and even certain cancers.
Healthcare providers may recommend an RF test if you have symptoms such as joint pain, joint swelling, fatigue, low fever, and unexplained weight loss.
A rheumatoid factor test can detect the presence of rheumatoid factor, an antibody that may mistakenly attack healthy cells and tissues. The body may produce RF as a result of an abnormal immune reaction. Having RF in your blood doesn’t always indicate an autoimmune disease, but its presence is a potential sign.
The RF test most often helps to diagnose rheumatoid arthritis (RA). Symptoms of RA usually begin in one or both sides of the wrist, hand, or foot joints. A healthcare provider may suggest an RF test if you have common symptoms of RA, including:
- Tenderness and swelling in the joint
- Joint pain
- Joint stiffness
- Fatigue
- Low fever
- Weight loss
Healthcare providers may also recommend the RF test to diagnose other autoimmune conditions and infections associated with high levels of rheumatoid factor. These conditions include:
- Sjögren syndrome
- Juvenile idiopathic arthritis (JIA)
- Systemic lupus erythematosus (SLE)
- Tuberculosis
- Hepatitis C
The blood test may also help to detect certain types of cancer, including leukemia and lung cancer.
You don’t need any special preparation for the rheumatoid factor test. However, check with your healthcare provider to see if you have any other tests that require fasting before the appointment. You should also ask whether you can continue taking your medications or supplements before the test.
The RF test usually takes place at a diagnostic laboratory or your provider’s office. Wear comfortable, loose-fitting clothing that allows easy access to your arm when it’s time to draw blood. You may consider bringing a family member or friend on the day of the test if blood tests make you anxious.
If you have insurance, talk to your insurance provider to see if they will cover the test’s cost or if you will need to pay out of pocket.
The rheumatoid factor test involves drawing a small sample of blood from a vein in your arm. The provider doing the blood draw will usually use a vein at the inside of the elbow, though they might use one on the back of your hand. The process usually takes less than five minutes.
During the Test
During the test, you will sit in a chair while a phlebotomist (a medical professional trained to draw blood) uses a needle to take blood from a vein in your arm. Here is what the provider will do during a blood draw:
- Clean the area with antiseptic
- Put an elastic band on the upper arm to put pressure on the area
- Insert the needle into a vein and collect blood in an airtight vial or tube attached to the needle
- Remove the needle and band from your arm
- Put a cotton pad or bandage on the needle site
You may feel a little sting when the needle goes in and out, but these symptoms go away quickly.
After the Test
You can go home almost immediately after the test and resume your daily activities. If you tend to feel weak and dizzy after blood tests, it may be best to ask someone to drive you home. Your healthcare provider may ask you not to lift any heavy objects for 24 hours after the test, since it can put strain on the needle site.
Blood tests are usually quite safe. You may experience slight pain or bruising at the needle site, but these symptoms go away quickly.
There may be some rare complications, including bleeding, infection at the needle site, or nerve damage. It’s important to contact your healthcare provider if these complications arise.
The results of a rheumatoid factor test are usually available within a few hours to a few days of the test. Some labs have an online portal where you can check the results. You may need to visit your healthcare provider to discuss the results and determine if you need further tests.
Interpreting Your Results
Rheumatoid factor results will be listed in either international units per milliliter or as a titer. A titer is a measurement of the concentration of a substance in a solution and is displayed as a ratio.
The normal range of rheumatoid factor in blood is usually below 15 international units per milliliter or a titer of 1 to 80. The normal range may vary slightly depending on different laboratories.
A higher-than-normal range is indicative of a positive result, while a lower-than-normal range suggests a negative result.
Positive Result
A positive result means you have a higher-than-normal level of rheumatoid factor in your blood. It may be a sign of rheumatoid arthritis, other autoimmune diseases, or an underlying infection.
Your healthcare provider may recommend additional tests to confirm what’s causing the positive RF test. These include:
- C-reactive protein test
- Erythrocyte stimulation rate (ESR) test
- Anticyclic citrullinated peptide (anti-CCP) antibody test
- Antinuclear antibody (ANA) test
Negative Result
A negative result means you have little or no rheumatoid factor in your blood. However, it does not rule out the presence of rheumatoid arthritis or other conditions. In some cases, people with RA do not have high levels of rheumatoid factor in their blood.
If you have low levels of RF in your blood but still have joint pain or other symptoms, talk to your healthcare provider about additional testing.
The rheumatoid factor test measures the levels of RF antibodies in your blood. It can help diagnose conditions like rheumatoid arthritis and Sjögren syndrome.
A healthcare provider may order an RF blood test if you have symptoms like joint swelling, joint pain, and fatigue.
High RF levels may indicate you have a condition that needs further diagnostic testing.
