Rheumatoid factor test is used by health-care professionals to help in diagnosing rheumatoid arthritis. Sometimes rheumatoid factor can be detected in the blood of normal individuals and of those with other autoimmune diseases that are not rheumatoid arthritis. In people with rheumatoid arthritis, high levels of rheumatoid factor can indicate a tendency toward more aggressive disease and/or a tendency to develop rheumatoid nodules and/or rheumatoid lung disease. Rheumatoid factor is an antibody that is measurable in the blood with a routine blood test. Rheumatoid factor is actually an antibody that can bind to other antibodies. Antibodies are normal proteins in our blood that are important parts of our immune system. Rheumatoid factor is an antibody that is not usually present in the normal individual. Because rheumatoid factor antibody binds to normal antibodies, it can be generally referred to as an autoantibody. Health-care professionals use the rheumatoid factor test to assist in the diagnosis of rheumatoid arthritis. Rheumatoid factor is sometimes abbreviated as "RF."