The distribution of joint inflammation is important to the doctor in making a diagnosis. In rheumatoid arthritis, the small joints of the hands, wrists, feet, and knees are typically inflamed in a symmetrical distribution (affecting both sides of the body). When only one or two joints are inflamed, the diagnosis of rheumatoid arthritis becomes more difficult. The doctor may then perform other tests to exclude arthritis due to infection or gout. The detection of rheumatoid nodules (described above), most often around the elbows and fingers, can suggest the diagnosis.

   Abnormal blood antibodies can be found in patients with rheumatoid arthritis. A blood antibody called "rheumatoid factor" can be found in 80% of patients. Citrulline antibody (also referred to as anti-citrulline antibody, anti-cyclic citrullinated peptide antibody, and anti-CCP) is present in most patients with rheumatoid arthritis. It is useful in the diagnosis of rheumatoid arthritis when evaluating patients with unexplained joint inflammation. A test for citrulline antibodies is most helpful in looking for the cause of previously undiagnosed inflammatory arthritis when the traditional blood test for rheumatoid arthritis, rheumatoid factor, is not present. Citrulline antibodies have been felt to represent the earlier stages of rheumatoid arthritis in this setting. Another antibody called "the antinuclear antibody" (ANA) is also frequently found in patients with rheumatoid arthritis.

   A blood test called the sedimentation rate (sed rate) is a measure of how fast red blood cells fall to the bottom of a test tube. The sed rate is used as a crude measure of the inflammation of the joints. The sed rate is usually faster during disease flares, and slower during remissions. Another blood test that is used to measure the degree of inflammation present in the body is the C-reactive protein. The rheumatoid factor, ANA, sed rate, and C-reactive protein tests can also be abnormal in other systemic autoimmune and inflammatory conditions. Therefore, abnormalities in these blood tests alone are not sufficient for a firm diagnosis of rheumatoid arthritis.

   Joint x-rays may be normal or only show swelling of soft tissues early in the disease. As the disease progresses x-rays can show bony erosions typical of rheumatoid arthritis in the joints. Joint x-rays can also be helpful in monitoring the progression of disease and joint damage over time. Bone scanning, a radioactive test procedure, can demonstrate the inflamed joints.

   The doctor may elect to perform an office procedure called arthrocentesis. In this procedure, a sterile needle and syringe are used to drain joint fluid out of the joint for study in the laboratory. Analysis of the joint fluid, in the laboratory, can help to exclude other causes of arthritis, such as infection and gout. Arthrocentesis can also be helpful in relieving joint swelling and pain. Occasionally, cortisone medications are injected into the joint during the arthrocentesis in order to rapidly relieve joint inflammation and further reduce symptoms.

   There is no single test that can confirm the diagnosis of rheumatoid arthritis. Your health care provider will use the results of your interview and physical examination, lab tests, and imaging studies such as x-rays to determine whether you have rheumatoid arthritis. At any time in the process of making the diagnosis or treating the condition, your primary care provider may refer you to a rheumatologist (a specialist in diagnosing and treating rheumatic diseases such as rheumatoid arthritis).

Lab tests: Your health care provider may run any of the following tests:

• Complete blood count: This test measures how many of each type of blood cell are in your blood. This will show anemia as well as other irregularities that could indicate rheumatoid arthritis.
• Markers of inflammation: These include measures such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). Levels of both of these are usually high in rheumatoid arthritis and may be good indicators of the extent of disease activity at any given time.
• Other blood tests: Levels of electrolytes (such as calcium, magnesium, and potassium) and proteins may be tested. Kidney and liver functions also may be checked.
• Immunologic tests: Levels of rheumatoid factor (RF), antinuclear antibodies (ANA), and possibly other antibodies (anti-RA33, anti-CCP) may be checked. The majority of people have a positive RF result during the disease’s active periods. A positive ANA result indicates an unusually active immune system. About 40% of people with rheumatoid arthritis have a positive ANA result. In the first few months of onset of rheumatoid arthritis, these immunologic tests may be negative, and, in some patients, they are always negative.

Synovial fluid analysis: The synovium produces fluid that helps lubricate and protect joints. Like blood, this fluid may be abnormal in rheumatoid arthritis. It may reveal characteristic signs of inflammation that point to rheumatoid arthritis, such as white blood cells. A sample of this fluid is withdrawn from a joint (usually the knee) through a needle in a procedure called arthrocentesis, or joint aspiration. The fluid is examined and analyzed for signs of inflammation.

Imaging studies: X-rays and sometimes other imaging studies often are used to detect damage to the joints.

• X-rays: X-rays may be taken of sites where symptoms or signs occur. Early in rheumatoid arthritis, the x-ray may be normal or show only soft tissue swelling, but damage can still be occurring. Over time, the usual finding is erosion of the bony part of the joint. These changes are distinguishable from changes seen with other types of arthritis such as osteoarthritis.
  
• MRI: MRI may allow earlier detection of bone erosion than x-rays.
• Ultrasound: Ultrasound uses high-frequency sound waves to take pictures of structures inside the body. It can be used to examine and to detect abnormal collections of fluid (effusions, which cause swelling) in the soft tissues around joints that are not easily accessible (such as hip joints or shoulder joints in obese patients).
• Bone scanning: In this test, a special picture of the entire skeleton is taken after a harmless radioactive isotope is injected into a vein. Diseased or damaged bone takes up the radioisotope in a different way than healthy bone and gives a characteristic picture. This technique may be used to detect inflammatory changes in bone.
• Densitometry: This scan detects changes in the thickness of bone that may indicate osteoporosis.
• Arthroscopy: A small scope, a long narrow tube with a light and a camera on the end, is used to examine the inside of the joint. The scope is inserted through a small incision in the skin. The camera transmits pictures to a video monitor, allowing the doctor to detect signs of rheumatoid arthritis or other joint disease. This test is not always necessary.

Classification

The American College of Rheumatology has developed a system for classifying rheumatoid arthritis. This system helps medical professionals determine the severity of your rheumatoid arthritis.

Stage I

• No damage seen on x-rays, although there may be signs of bone thinning

Stage II

• On x-ray, evidence of bone thinning around a joint with or without slight bone damage
• Slight cartilage damage possible
• Joint mobility may be limited; no joint deformities observed
• Atrophy of adjacent muscle
• Abnormalities of soft tissue around joint possible

Stage III

• On x-ray, evidence of cartilage and bone damage and bone thinning around the joint
• Joint deformity without permanent stiffening or fixation of the joint
• Extensive muscle atrophy
• Abnormalities of soft tissue around joint possible

Stage IV

• On x-ray, evidence of cartilage and bone damage and osteoporosis around joint
• Joint deformity with permanent stiffening or fixation of the joint (ankylosis)
• Extensive muscle atrophy
• Abnormalities of soft tissue around joint possible

Rheumatologists also classify the functional status of persons with rheumatoid arthritis, as follows:

• Class I - Completely able to perform usual activities of daily living
  
• Class II - Able to perform usual self-care and work activities but limited in activities outside of work (such as playing sports, household chores)
  
• Class III - Able to perform usual self-care activities but limited in work and other activities
  
• Class IV - Limited in ability to perform usual self-care, work, and other activities