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Arthritis Test Results

Joint Fluid Tests

The blood is not the only bodily fluid that holds clues to the type of arthritis you have. Sometimes doctors order tests to analyze samples of joint fluid, also called synovial fluid. Doctors draw joint fluid from the joint space with a needle; in a person with arthritis, the presence of bacteria suggests that joint inflammation is caused by bacteria. The presence of crystals can confirm a diagnosis of gout, a condition in which uric acid, a waste product, deposits as crystals in the joint tissue, causing intense pain and inflammation. Other types of crystals may indicate different diagnoses.

Limitations: Although joint fluid tests may help rule out a diagnosis of rheumatoid arthritis (for example, if a diagnosis of gout is confirmed), they cannot confirm an RA diagnosis. Analyzing the joint fluid may eventually be helpful in detecting markers of joint destruction in rheumatoid arthritis, but at present this is investigational and not widely done.


X-rays of the joints can be useful in diagnosing and monitoring many forms of arthritis, including rheumatoid arthritis, ankylosing spondylitis, and osteoarthritis. In people with ankylosing spondylitis, X-rays of the sacroiliac joint can help confirm a diagnosis early on. In rheumatoid arthritis, the early development of bony erosions is associated with more severe disease.

Limitations: Although X-rays are useful in the evaluation of rheumatoid arthritis, they lack the sensitivity to show damage early in the course of the disease when treatment to prevent further damage is critical. Also, X-rays only show joint and bony damage; other imaging tests are needed to examine soft tissues.

WebMD Medical Reference

Reviewed by David Zelman, MD on February 10, 2014
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