Rheumatoid factor (RF) is a blood test that helps to diagnose rheumatoid arthritis, lupus, and sarcoidosis. Elevated test results or high levels indicate severe disease. Learn about the normal range for rheumatoid factor.
Rheumatoid factors are proteins made by your immune system that can attack healthy tissue in your body. High levels of rheumatoid factor in the blood are most often related to autoimmune diseases such as rheumatoid arthritis and Sjögren’s syndrome. However, rheumatoid factor may be detected in some healthy individuals. Sometimes, people with autoimmune diseases do not show elevated levels of rheumatoid factor.
A positive rheumatoid factor test means that the level of rheumatoid factor in the patient’s blood is considered high. Rheumatoid factor was first described in relation to rheumatoid arthritis in 1940. For decades, a positive rheumatoid arthritis test was used to diagnose those with symptoms of rheumatoid arthritis.
An RF test looks for rheumatoid factor (RF) in a blood sample. Normally, your immune system makes proteins called antibodies to attack germs that could make you sick. But rheumatoid factors are antibodies that sometimes attack healthy cells and tissues in your body.
Rheumatoid factor is part of the immune system’s attack on healthy tissues and cells in the body, causing inflammation. It is possible to measure RF with a blood test. Since about 80% of adults with RA have rheumatoid factor, it is a common blood test during the diagnosis process.
A positive rheumatoid factor can be found in other conditions besides RA, like chronic infections. However, a very high level like this is a clue that RA might develop in the future, even if it is not present now. Therefore, someone with a very positive RF should be seen by a rheumatologist and followed periodically.
Rheumatoid factor is an autoantibody that is formed in people who have rheumatoid arthritis. It is a protein made by your immune system. High levels of RF in your blood indicate that you may have an autoimmune disease such as RA or Sjögren’s syndrome.
For more information, visit Mayo Clinic, MedicineNet, Medical News Today, RheumatoidArthritis.org, MedlinePlus, Verywell Health (1), Johns Hopkins Arthritis, and Verywell Health (2).
