Diagnosis

Osteoarthritis is often visible in x-rays. Cartilage loss is indicated by certain images:

• If the normal space between the bones in a joint is narrowed.
• If there is an abnormal increase in bone density.
• If bony projections, cysts, or erosions are evident.
• X-rays can also reveal any cysts that might develop in osteoarthritic joints. If other conditions are suspected or if the diagnosis is uncertain, additional tests are necessary.
• An MRI may show evidence of osteoarthritis that x-rays miss.

X-rays are a form of electromagnetic radiation (like light); they are of higher energy, however, and can penetrate the body to form an image on film. Structures that are dense (such as bone) will appear white, air will be black, and other structures will be shades of gray depending on density. X-rays can provide information about obstructions, tumors, and other diseases, especially when coupled with the use of barium and air contrast within the bowel.

Blood Tests

Blood test results may help diagnose or rule out osteoarthritis. Some examples include:

• Elevated levels of rheumatoid factor (specific antibodies in the synovium) and so-called erythrocyte sedimentation rates (ESR or sed rate) indicate rheumatoid arthritis.
• Hyaluronic acid (HA), a joint lubricant, is being tested as a potential biomarker for osteoarthritis. High levels of HA may indicate increased risk for osteoarthritis.
• Elevated levels of a factor called C-reactive protein, which is produced by the liver in response to inflammation, are proving to be good predictors of osteoarthritic progression in the knee.

Tests of the Synovial Fluid

If the diagnosis is uncertain or infection is suspected, a doctor may attempt to withdraw synovial fluid from the joint using a needle. There will not be enough fluid to withdraw if the joint is normal. If the doctor can withdraw fluid, problems are likely, and the fluid will be tested for factors that might confirm or rule out osteoarthritis:

• Cartilage cells in the fluid are signs of osteoarthritis
• A high white blood cell count is a sign of infection
• High uric acid in the fluid is an indication of gout

Click the icon to see an animation on gout.

• Other factors may be present that suggest different arthritic conditions, including Lyme disease and rheumatoid arthritis.
• In people with known osteoarthritis, researchers may look for certain factors in synovial fluid (sulfated glycosaminoglycan, keratin sulfate, and link protein) that can suggest a more or less severe condition.