Diagnosing Rheumatoid Arthritis - Rheumatoid Arthritis: Arthritis

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Diagnosing rheumatoid arthritis

People who have symptoms of arthritis should have a complete medical evaluation (see "Diagnosing arthritis"). The symptoms and physical examination are the most important parts of the diagnostic process. The early joint symptoms of other conditions, such as lupus, are sometimes indistinguishable from those of rheumatoid arthritis, making a definitive diagnosis difficult soon after symptoms start. Blood and imaging tests are often ordered to help with diagnosis.

It's important to understand that it may take several weeks (and several visits) before you receive a definite diagnosis. People often find it frustrating to wait, and they worry that they are not receiving prompt treatment. But you may find it reassuring to know that a few weeks' delay will not jeopardize your health, whereas undergoing the wrong therapy could.

Blood tests for rheumatoid arthritis

Your doctor may order several types of blood tests, because no one test is sufficient to confirm a diagnosis.

Rheumatoid factor. The vast majority (70%–80%) of people with rheumatoid arthritis have an abnormal antibody called the rheumatoid factor in their blood, so you will probably undergo a simple blood test for this antibody. Just be aware that if rheumatoid factor is detected in your blood (meaning the test is positive), it doesn't necessarily mean that you have rheumatoid arthritis. About 10% of people who do not have rheumatoid arthritis will test positive for rheumatoid factor. Such people may either be perfectly healthy or suffering from another disorder such as systemic lupus erythematosus (see "Related disorders"). At the same time, some people with rheumatoid arthritis will test negative for rheumatoid factor. Thus your doctor is likely to order additional blood tests to look for causes of joint pain.

Anti-CCP. The anticitrullinated cyclic protein (anti-CCP) test measures the presence of an antibody associated with rheumatoid arthritis. The anti-CCP test is gradually becoming more common. (Indeed, some rheumatologists now order it routinely whenever they order a rheumatoid factor test.) Some small early studies have shown that the anti-CCP test can reliably help to diagnose rheumatoid arthritis in three types of people: those with early-stage disease for whom uncertainty remains about diagnosis, those with mild symptoms who test negative for rheumatoid factor, and those who test positive for rheumatoid factor but may suffer from some other condition. Researchers do not yet know whether the anti-CCP test is useful in other circumstances, or whether the anti-CCP test offers much benefit beyond standard clinical tests.

ESR. The erythrocyte sedimentation rate (ESR) provides a measure of body-wide inflammation: The higher the rate, the greater the likelihood that you are suffering from inflammation, which could be caused by rheumatoid arthritis. This test can also help determine how serious your condition is.

CRP. The C-reactive protein (CRP) test also measures inflammation, but tends to change more rapidly than the ESR; minor elevations have also been associated with an increased risk of cardiovascular disease. In assessing inflammation due to rheumatoid arthritis, this test offers no clear advantages over the ESR.

Imaging tests for rheumatoid arthritis

Since rheumatoid arthritis often involves the hands and feet, your doctor may also order x-rays and possibly magnetic resonance imaging (MRI) of these joints and others to check for bone erosions. Initial studies of MRI show that it is better at detecting bone erosions than x-rays, but its use is controversial because it may detect cysts or other bone changes that resemble erosions, and thus could lead to unnecessary treatment. The issue is important, because rheumatoid arthritis is a disease that varies greatly in its progression and impact: Treatment should be directed by symptoms, findings on physical examination, the results of joint imaging, and preferences of the patient, not just by the results of a single imaging test. In addition, MRI is expensive, and routine use could drive up the cost of caring for people with rheumatoid arthritis dramatically.

Last updated:	September 05, 2008