Diagnosis of rheumatoid arthritis (RA) includes a combination of detailed medical history, physical examination, laboratory tests and imaging studies. Patients may be asked to complete a pain assessment form. There is not one specific test that can definitively diagnose the disease.

During the physical examination, the joints will be checked for swelling, warmth, tenderness and range of motion. The physician notes descriptions and incidences of pain and its duration. The physician may try to move various joints to see if motion causes pain. The diagnosis will also include a medical history, including any family history of arthritis or autoimmune conditions, previous injuries or surgeries and general use of the joints, including stiffness in the morning lasting more than one hour.

RA may be difficult to distinguish from other arthritic disorders. A primary care physician who suspects or diagnoses RA may refer may refer the patient to a rheumatologist, a physician who specializes in arthritis and other diseases of the muscles, joints and bones. Several other conditions may have symptoms similar to RA and must be ruled out. These conditions include other forms of arthritis and lupus.

Many laboratory tests are used to screen for specific kinds of arthritis or other diseases. Certain blood tests frequently produce characteristic results in RA patients, but do not definitively diagnose RA. Some of these blood tests include:

• Complete blood count (CBC). This routine blood test measures the levels of different types of blood cells. People with RA may show a low count of red blood cells (anemia) and higher counts of white blood cells and platelets.
  
  
• Erythrocyte sedimentation rate (ESR or sed rate). A high ESR indicates inflammation, which may be due to many causes.
  
  
• C reactive protein test. An elevated level of this protein produced by the liver suggests an inflammatory disease such as RA.
  
  
• Antinuclear antibody (ANA) test. Tests for certain autoimmune disorders such as RA and systemic lupus erythematosus.
  
  
• Rheumatoid factor (RF) test. Identifies the presence of the RF antibody. This may indicate RA or other autoimmune conditions such as Sjogren's syndrome, which is characterized by dry eyes and dry mouth. The test may be negative in early stages of RA or when the disease is in remission, with no flare-ups of inflammation. This antibody is usually present in 60 percent of patients in the first year of disease and in 80 percent of patients who have chronic RA.
  
  
• Cyclic citrullinated peptide antibody (CCP) test. Identifies the presence of an antibody to citrulline, an amino acid. This test may identify RA at an earlier stage than the RF test. The CCP test may be ordered along with the RF test, or after a patient with symptoms has tested negative for RF.

Another test commonly used for RA is a synovial fluid analysis. Fluid from an affected joint is withdrawn with a needle (a procedure called arthrocentesis). In addition to RA, the fluid may indicate gout, infectious arthritis or juvenile rheumatoid arthritis.

A diagnostic examination where RA is suspected may also include x-rays. However, when RA is in its early stages, x-rays may not show much disease. X-rays are useful to differentiate RA from osteoarthritis, which is much more apparent in early x-rays. Images taken in early stage RA can serve as a baseline to monitor the changes in the joints. MRI (magnetic resonance imaging) and ultrasound provide better views of the soft tissues but are not commonly used. Ultrasounds may be useful for RA in the hands.

The American College of Rheumatology has established criteria for clinical classification of RA:

1. Morning joint stiffness for more than one hour
2. Swelling of three or more joint areas simultaneously
3. Swelling in the wrist or two of the three finger joints
4. Swelling of the same joints on both sides of the body
5. Rheumatoid nodules
6. Positive blood test for rheumatoid factor
7. X-ray changes that include erosions or decalcification of bones near joints

Patients can be classified as having RA if they have four or more of the criteria listed. The first four listed must have been present for at least six weeks.