What Is Rheumatoid Factor?
My doctor wants to test me for rheumatoid factor because she thinks my joint pain may be caused by rheumatoid arthritis. What is rheumatoid factor? How does it relate to rheumatoid arthritis?
There is no one single test that a healthcare provider can use to make a rheumatoid arthritis diagnosis, so he or she will use a combination of tests. One common test is for rheumatoid factor, an antibody (a special protein made by the immune system that normally helps fight foreign substances in the body) that is present eventually in the blood of most people with rheumatoid arthritis.
However, not all people with this condition test positive for rheumatoid factor. This is especially true early in the disease. Also, some people test positive for rheumatoid factor, yet never actually develop the disease. Testing positive or negative for rheumatoid factor doesn't necessarily confirm or rule out an RA diagnosis. It is simply one more piece in the puzzle.