What is it? An RF is a blood test that measures the level of a protein in the blood called rheumatoid factor. High levels, called high titers, of RF in the blood can indicate rheumatoid arthritis, as well as other diseases.
What the results show. High RF levels can be found in up to 80% of people who have rheumatoid arthritis. The results of this test may help your doctor rule out rheumatoid arthritis. High levels of RF and a confirmed rheumatoid arthritis diagnosis can indicate a more severe disease. In addition, RF is sometimes found in the blood in a small percentage - about 5% - of people who have no disease whatsoever. This is why your doctor must use the RF test along with the physical exam, medical history, and possibly X-rays before making a diagnosis of rheumatoid arthritis.