There are more than 100 types of arthritis. Some show up on an x-ray while others may not. For example, osteoarthritis is usually easy to see on an x-ray. But arthritis due to lupus may not appear.
Here are some other difficulties with x-rays. Joint damage due to a bacterial infection may take a week or more to appear on an x-ray. It may take three or more months for damage related to rheumatoid arthritis to be seen on an x-ray. Arthritis missed by x-rays may show up on an MRI and a CT scan.
A number of other tests can be helpful in the diagnosis of arthritis. But keep in mind that in many cases, no testing is needed to confirm the diagnosis or identify a cause. A careful review of a patient's symptoms and thorough examination may be all that's needed.
When testing is needed, the most useful test depends on which type of arthritis is suspected. For example, commonly used tests for arthritis include:
- Measures of inflammation
Blood tests for erythrocyte sedimentation rate and C-reactive protein help predict the presence of a systemic (body-wide) inflammatory disease as the cause of arthritis. For example, an elevated level of one or both of these tests is common in rheumatoid arthritis or lupus. Normal values are typical of osteoarthritis.
- Autoantibody tests
Rheumatoid factor and anti-cyclic citrullinated protein are often present in the blood of people with rheumatoid arthritis while anti-nuclear antibodies are highly associated with lupus or related conditions.
- Uric acid levels
An elevated blood uric acid level increases that chances (though it does not prove) that gout is the cause of arthritis.
- Joint fluid analysis
When the cause of arthritis is not certain, joint fluid may be removed and tested for look for infection or crystals (such as gout or calcium crystals). A high white-blood cell count in the joint fluid can also provide information about how much inflammation is present.
- Antibody tests for infection
Blood levels of specific antibodies for viral infections (such as hepatitis B, hepatitis C, or parvovirus) or Lyme disease can be useful when these conditions are suspected.
- Genetic testing
Blood testing for the genetic marker HLA-B27 may be needed when ankylosing spondylitis is suspected. Approximately 95% of people with this form of spinal arthritis carry this genetic variant.
In cases where the cause of arthritis is uncertain despite extensive evaluation, surgically removing a small sample of joint tissue can be quite useful. This is especially true when an infection, such as tuberculosis, is a concern.
And this is only a partial list!
None of these tests are perfect. Some people with arthritis have normal test results and some people without arthritis have abnormal results. This can make it challenging to interpret test results. So, if you and your doctor are concerned that you may have arthritis, the best approach is to review your symptoms and examination findings in detail and then, if necessary, have only the tests that are most accurate for the conditions that seem mostly likely.