A diagnosis of arthritis is the first step toward arthritis treatment. In addition to arthritis symptoms and a doctor's examination, blood tests and X-rays are commonly used to confirm rheumatoid arthritis. Most people with rheumatoid arthritis have antibodies called rheumatoid factors (RF) in their blood, although RF may also be present in other disorders.
X-rays are used to diagnose osteoarthritis, typically revealing a loss of cartilage, bony spurs, and bone rubbing against bone. Sometimes blood tests and joint aspiration (using a needle to draw a small sample of fluid from the joint for testing) are used to rule out other types of arthritis. If your doctor suspects infectious arthritis as a complication of some other disease, testing a sample of fluid from the affected joint will usually confirm the diagnosis.
WebMD. (2009, November 20). Retrieved from http://arthritis.webmd.com/understanding-arthritis-treatment