How is rheumatoid arthritis diagnosed?

The first step in the diagnosis of rheumatoid arthritis is a meeting between the doctor and the patient. The doctor reviews the history of symptoms, examines the joints for inflammation and deformity, the skin for rheumatoid nodules, and other parts of the body for inflammation. Certain blood and X-ray tests are often obtained. The diagnosis will be based on the pattern of symptoms, the distribution of the inflamed joints, and the blood and x-ray findings. Several visits may be necessary before the doctor can be certain of the diagnosis. A doctor with special training in arthritis and related diseases is called a rheumatologist.

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.