Your doctor may suspect rheumatoid arthritis (RA) based on your symptoms. Diagnosing RA can sometimes be difficult since there are several autoimmune disorders that have similar symptoms. Part of diagnosing RA is ruling out these other disorders.

The American College of Rheumatology and the European League Against Rheumatism have created a system for diagnosing RA. To start, symptoms need to be present for 6 weeks or more. The system then uses a 10-point scale assessing specific symptoms. The higher the score, the more likely RA is present.

Considered factors include:

Joint Involvement

The number of sore or swollen joints and any associated damage is considered. The areas affected may be a small joint ( hands or feet) or a large joint (shoulders, elbows, hips, knees, or ankles). Which joints are affected, how many joints are affected, and for how long they have been affected all help with the diagnosis.

Blood Tests

Blood tests look for markers of RA. Specific substances that may be present with RA can be found in the blood. These include:

    
  • Rheumatoid factor (RF)—An autoantibody (factor that marks own tissue for attack by immune system) associated with RA and other autoimmune disorders.
  • Anti-citrullinated protein antibody—Autoantibodies that are directed to proteins.
  • Erythrocyte sedimentation rate (ESR)—To measure inflammation. Faster ESR rates are seen in many different diseases.
  • C-reactive protein (CRP)—A protein found in the blood that rises in response to inflammation.
  • Imaging Tests

    Imaging tests assess the joints, surrounding structures, and any associated damage. Tests may include:

        
  • X-rays
  • Ultrasound
  • MRI scan
  • Other Tests

    The following tests involve tissue samples. The samples are examined under a microscope. They can help diagnose RA (and other conditions).

        
  • Synovial biopsy—Removing a piece of the synovial membrane that lines the joint capsule.
  • Arthrocentesis (joint aspiration)—Removal of synovial fluid from the joint with a needle.