Your doctor will determine if you have ankylosing spondylitis (AS) by performing a physical examination, taking a detailed history of your symptoms, medical history, and family history, and looking at the results of lab tests and X-rays.

In the physical examination, your doctor will look for the sites of inflammation and tenderness along your back, pelvic bones, chest, buttocks, and heels. Your doctor may also check for any limitations in your mobility or chest expansion.

Your doctor may take images of your spine using radiographic tests: X-rays or MRI (magnetic resonance imaging, which uses a magnetic field and radio frequency pulses to view tissues and organs inside the body). An MRI can show signs of inflammation. X-rays can show spine damage, especially to the sacroiliac joints, but it may take several years for this to be evident on the X-ray.

A test for the presence of the HLA-B27 gene that is found in 90% of people with AS can be performed. The presence of HLA-B27 does not mean a diagnosis of AS, but a doctor may use this test to help detect AS early. Your doctor may also order a blood test to look for signs of inflammation in the body.