X-rays and lab tests

An X-ray of a joint that is affected by OA can show narrowing of the joint space. Other abnormalities include "osteophytes," bony growths at the joint that look like little bumps. However, X-rays are not conclusive for diagnosis, because a lot of people experience the pain of OA before changes become apparent. Conversely, an X-ray might show physical changes associated with OA in people who do not report pain or other symptoms.

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A test called joint aspiration can be used to rule out other illnesses. Under a local anesthetic, a doctor inserts a fine needle into the joint and withdraws a small amount of joint fluid. This fluid can be examined for bacteria or signs of infectious arthritis, inflammation of a joint caused by an infection. It can also be examined for crystals of uric acid, which indicate yet another disease known as gout.

Similarly, blood tests don't indicate OA but can be used to rule out rheumatoid arthritis. A person with rheumatoid arthritis often has substances in the blood that indicate a systemwide inflammation, while a person with OA does not.