Rheumatoid Factor (RF) Test
Reviewed
Also called: Rheumatoid Factor Blood Test, RF Blood Test
A rheumatoid factor (RF) test checks a sample of your blood for rheumatoid factor, a protein made by the immune system.
Specimen: blood
Why this test may be ordered
- To help diagnose rheumatoid arthritis when symptoms are present
- To check for other autoimmune disorders, chronic infections, or certain types of cancer
- When patients have anemia, as people with rheumatoid arthritis often develop anemia
Preparation and collection
You don't need any special preparations for an RF test.
A health care professional will take a blood sample from a vein in your arm, using a small needle. This usually takes less than five minutes. If you do a home test, remember to share your results with your provider.
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
Understanding results
The results of an RF test alone cannot diagnose a condition. Generally, your results will be either positive or negative.
- Negative (normal): A negative (normal) result means that you have little or no rheumatoid factor in your blood. Limitation: But that doesn't rule out rheumatoid arthritis or another health problem. Next step: If you have symptoms of rheumatoid arthritis, but your RF test results are normal, your provider may order more tests to make a diagnosis.
- Positive (abnormal): A positive (abnormal) result means that a higher level of rheumatoid factor was found in your blood. Limitation: Similarly, people without rheumatoid arthritis can have a lot of RF in their blood. Next step: However, your provider can use these results, along with your medical history and the results of other tests, to determine if you have rheumatoid arthritis or any other condition that causes high RF levels.
- A positive RF result alone cannot diagnose a condition; it must be interpreted with medical history and other tests.
- A negative RF result does not rule out rheumatoid arthritis or other health problems.
- People with rheumatoid arthritis can have little or no RF, while people without rheumatoid arthritis can have high RF levels.
What to do next
Your provider may refer you to a rheumatologist (a provider who specializes in autoimmune disorders, including RF) to get more testing if your results are inconclusive.
- Joint pain or stiffness when moving, especially worse in the morning or after inactivity
- Joint tenderness, redness, and warmth
- Joint swelling that makes daily activities hard
- Fatigue, fever, and loss of appetite
- Hard bumps under the skin near joints
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: Rheumatoid Factor (RF) Test