How Do Doctors Test for Ankylosing Spondylitis?

diagnosing ankylosing spondylitis
Diagnosing ankylosing spondylitis (AS) is done through a physical exam, blood tests, and imaging studies

Ankylosing spondylitis is usually diagnosed by rheumatologists, who are doctors that specialize in diseases related to the bones, muscles, and joints. 

Your doctor may first take a detailed history and conduct a physical exam. They will ask you about your symptoms, how and when they appeared, and their severity. Since ankylosing spondylitis can run in families, your doctor may also ask whether anyone in your family (parents, grandparents or siblings) has or had the disease. They will also examine you to look for any signs of joint inflammation, stiffness, pallor, and eye or skin involvement.

Your doctor will then test for ankylosing spondylitis by ordering for the following:

  • Blood work and the HLA-B27 test: Your blood sample may be analyzed for blood counts, erythrocyte sedimentation rate (ESR), and other inflammatory markers, such as C-reactive protein (CRP). Your doctor may also order an analysis of your blood to test for HLA-B27, a protein that may be raised in people with ankylosing spondylitis. Blood tests can also rule out other causes for the symptoms, such as rheumatoid arthritis or lupus.
  • Imaging studies: These are done to look for the involvement of joints and bones by the disease. Tests include X-rays, computed tomography (CT) scans, and magnetic resonance imaging (MRI) scans.

What is ankylosing spondylitis?

Ankylosing spondylitis is a type of arthritis (joint inflammation) affecting the spine. 

The spine is made up of a series of ring-like bones called the vertebrae. With ankylosing spondylitis, the vertebrae and joints between the spine and pelvis become inflamed. The condition may also affect other joints in the ribs, knees, neck, and feet

Besides joints, ankylosing spondylitis can also affect other sites, such as the eyes, skin, heart, lungs, and kidneys.

Ankylosing spondylitis affects around 0.2%-0.5% of people in the U.S. The disease is more common (almost twice as common) and more severe in men as compared to women. 

What are signs and symptoms of ankylosing spondylitis?

Symptoms of ankylosing spondylitis vary from person to person. Generally, the symptoms first appear during late adolescence or early adulthood (between 17-45 years of age). In some people, however, the symptoms start appearing in childhood or much later in life. 

Symptoms usually begin gradually over weeks or months and present as lower back/buttocks pain and stiffness. For some people, initial symptoms may begin from other sites, such as the neck. Atypical presentation is more common in women and may make diagnosis difficult. 

During the initial stages of the disease, there may be:

  • Mild fever
  • Loss of appetite
  • Feeling of being sick
  • Pain felt on one side of the body at a time
  • Pain that is dull and diffused rather than sharp or localized
  • Pain that is worse in the morning and may cause you to wake up from sleep in the second half of the night. 
  • Pain that is worse when resting and improved when moving or taking a warm shower

As the disease progresses:

  • Pain and stiffness become persistent and are felt on both sides of the body
  • Stiffness may spread upward and involve the neck as well
  • Over months or years, pain may be felt on several sites, such as the chest (ribs), shoulders, hips, heels, and thighs

Other symptoms include the following:


Back Pain: 16 Back Pain Truths and Myths See Slideshow
Johns Hopkins Arthritis Center. Ankylosing Spondylitis.

Spondylitis Association of America. Diagnosis of Ankylosing Spondylitis.