The rheumatoid factor (RF) test is a type of blood test used to screen for underlying disease or inflammation in the body. The test measures the presence and levels of rheumatoid factor, a type of antibody, in a patient’s blood sample.

The RF test is often used to help diagnose rheumatoid arthritis. It may also be used in the diagnosis of other inflammatory conditions, such as systemic lupus erythematosus, Sjogren’s syndrome or sarcoidosis.

However, RF test results alone are not used to diagnose these conditions because the presence of RF is not always indicative of disease or inflammation. Sometimes healthy people, especially the elderly, may test positive for RF. In addition, a negative result for RF does not rule out the presence of disease. This is because RF may not be reactive for months after an illness begins.

To confirm a diagnosis, physicians will use the RF test in conjunction with a physical examination, medical history and other tests.