Rheumatoid Factor (RF)

The rheumatoid factor (RF) blood test measures the level of the rheumatoid factor antibody in the blood.  The rheumatoid factor antibody is not usually present in the blood of health individuals.  The rheumatoid factor blood test is commonly used for the diagnosis of rheumatoid arthritis being present in about 80% of adults with rheumatoid arthritis.

Rheumatoid factor is sometimes found in the blood of individuals with other conditions including lupus, hepatitis, syphilis, tuberculosis, and liver disease.  Rheumatoid factor is also occasionally found in healthy individuals, particularly those with family members who have rheumatoid arthritis.