Rheumatoid Factor

The test detects rheumatoid factor (RF) in your blood. This protein is part of a normal immunogenic response to the presence of a foreign entity, such as bacteria or a virus, forming a complex that the immune system can remove.

If you have rheumatoid arthritis (RA) you will develop an abnormal protein called an autoantibody, which can result in RA at high levels. While normal antibodies attack pathogens like bacteria and viruses, autoantibodies such as RF mistakenly attack the body’s healthy cells and tissues.

Testing for RF is most often used in conjunction with other laboratory and imaging tests to diagnose RA or Sjögren’s syndrome. Some patients with RA may have low levels of RF, while 4% of some healthy people can have a positive RF.