Diagnosis of arthritis will involve a physical examination. A physician will examine the joints and muscles for tenderness and range of motion and note descriptions and incidences of pain and its duration. The diagnosis will also include a review of a medical history of any familial arthritic, rheumatic or autoimmune conditions, previous injuries or surgeries and general use of the joints. The patient may be asked to complete a pain assessment form.

Most diagnostic examinations where arthritis is suspected will include imaging studies. X-rays show the bones and joints and may indicate bony outgrowths or changes in the size of joint capsules or the position of bones. MRI (magnetic resonance imaging) and ultrasound images provide better views of the soft tissues. Ultrasounds may be useful for rheumatoid arthritis (RA) in the hands. Although x-rays are especially useful for osteoarthritis, they may be also used for suspected cases of RA to provide a baseline image.

Certain kinds of tests may be used to rule out conditions or specifically diagnose one form of arthritis. Many laboratory tests are used to screen for specific kinds of arthritis or other disease. Some of the blood tests include:

• Complete blood count. Helps test for infectious arthritis, as white blood cells usually increase with this form of arthritis.
  
  
• Antinuclear antibody (ANA) test. Helps test for certain autoimmune disorders such as RA and lupus.
  
  
• Rheumatoid factor (RF) test. May indicate RA or other autoimmune conditions. The test may be negative in some RA cases when the disease is in remission, with no flare-ups of inflammation.
  
  
• HLA-B27 test. Presence of this genetic marker in the white blood cells may indicate many conditions, including ankylosing spondylitis, RA, juvenile rheumatoid arthritis and Reiter’s syndrome.
  
  
• Erythrocyte sedimentation rate (ESR). An elevated level of this blood test indicates inflammation, but can be caused by many forms of inflammation or infection.
  
  
• C reactive protein test. An elevated level of this protein produced by the liver suggests an inflammatory disease such as RA.
  
  
• Uric acid. A high level of uric acid in the blood may indicate gout. Uric acid may also be measured through a urine test.

Tests that analyze the synovial fluid from a joint may indicate gout, infectious arthritis or juvenile rheumatoid arthritis. Arthroscopy may be performed to examine a joint. A tissue sample of skin or muscle may be taken for a biopsy when forms of arthritis that involve the skin or muscle, such as psoriatic arthritis, are suspected.

Few laboratory tests aid in diagnosis of osteoarthritis, but they may be used later to monitor the effects of drugs used for treatment. The combination of findings from lab tests and a physical examination may provide a physician with enough information to diagnose a specific form of arthritis.