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 that attacks healthy cells. It is mostly used with other tests to help diagnose rheumatoid arthritis. Results are either negative (normal) or positive (abnormal), but they cannot diagnose a condition alone. The provider uses results with medical history and other tests to determine a diagnosis.
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
No special preparations needed.
blood
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
RF test results can help diagnose rheumatoid arthritis and other autoimmune disorders, chronic infections, or certain cancers. Only a healthcare provider can interpret results along with other information.
- Negative: Negative or normal: Little or no rheumatoid factor detected in your blood. Limitation: A negative result does not rule out rheumatoid arthritis or another health problem. If symptoms persist, more tests may be ordered. Next step: Routine
- Positive: Positive or abnormal: Higher level of rheumatoid factor found in your blood. May be associated with rheumatoid arthritis, other autoimmune diseases, chronic infections, or certain cancers. Limitation: A positive result does not confirm a diagnosis by itself; your provider will consider other test results, symptoms, and medical history. Next step: Prompt
- 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 will use your RF results along with your medical history and results of other tests to determine if you have rheumatoid arthritis or another condition. If results are inconclusive, your provider may refer you to a rheumatologist for further testing.
- 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
U.S. National Library of Medicine: Rheumatoid Factor (RF) Test