Your doctor will use a medical history, physical exam, and X-ray to diagnose ankylosing spondylitis.

By asking questions about your medical history, your doctor can evaluate your symptoms. Most people with ankylosing spondylitis have back pain with four or five of the following characteristics:

• Begins before the age of 35
• Starts and worsens gradually
• Persists for at least 3 months
• Is associated with morning stiffness that usually lasts for more than one hour
• Improves with exercise

Your doctor will want to know whether you have any family members with ankylosing spondylitis or a related joint disease; 15% to 20% of people with ankylosing spondylitis have a family member with the same condition.² He or she may also ask whether you have had ongoing diarrhea, abdominal (belly) pain, multiple infections of the cervix (in women) or urethra (more common in men), psoriasis, or inflammation of the eye chamber (uveitis). These could be clues to having a condition other than ankylosing spondylitis.

You will have a physical exam to see how stiff your back is and whether you can expand your chest normally. Your doctor will also look for tender areas, especially over the points of the spine, the pelvis, the areas where your ribs join your breastbone, and your heels. You may experience chest pain and stiffness with ankylosing spondylitis.

Tests related to ankylosing spondylitis include:

• X-rays of the spine and pelvis to check for bone changes (bony erosions, fusion, or calcification of the spine and sacroiliac joints). Certain changes in the sacroiliac joint confirm the diagnosis of ankylosing spondylitis, but those changes can take several years to develop enough to show on X-ray. MRI is more sensitive than X-ray. If no changes to the sacroiliac joints show on the X-ray but your doctor still suspects ankylosing spondylitis, an MRI may allow an earlier diagnosis. Ultrasound is being studied as a way to diagnose ankylosing spondylitis earlier.
• A genetic test (through a blood test), which may be done to determine the presence of a particular gene (HLA-B27) that is often associated with ankylosing spondylitis. Many people with the HLA-B27 gene will not develop ankylosing spondylitis, so having this test will not confirm whether you have the condition. But the test results can be helpful if your symptoms and physical exam have not clearly pointed to a diagnosis.