The rheumatoid factor (RF) test is primarily used to help diagnose rheumatoid arthritis (RA) and to help distinguish RA from other forms of arthritis or other conditions that cause similar symptoms. While diagnosis of RA relies heavily on the clinical picture, some of the signs and symptoms may not be present or follow a typical pattern, especially early in the disease. Furthermore, the signs and symptoms may not always be clearly identifiable since people with RA may also have other connective tissue disorders or conditions, such as phenomenon, scleroderma, autoimmune thyroid disorders, and systemic lupus erythematosis, and display symptoms of these disorders as well. The RF test is one tool among others that can be used to help make a diagnosis when RA is suspected.