Rheumatoid Factor (RF) Test
Reviewed
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.
Preparation and collection
No special preparations needed.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- 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.
Evidence source
U.S. National Library of Medicine: Rheumatoid Factor (RF) Test