Test Details: Rheumatoid Factor (RF) testing is mostly used with other tests to help diagnose rheumatoid arthritis. Rheumatoid arthritis (RA) is a type of autoimmune disorder that damages joints and causes pain, swelling and stiffness. It is a chronic condition that can also affect other organs. Rheumatoid factor levels may also increase significantly in other conditions, including chronic infections, inflammatory lung diseases such as sarcoidosis, mixed connective tissue disease, Sjogren's syndrome, Systemic lupus erythematosus, etc.