Ankylosing spondylitis is a type of arthritis that causes pain and stiffness in your spine and other joints. It typically affects your sacroiliac joint, where your spine and pelvis meet. Doctors diagnose this condition using a combination of symptoms, lab tests, and imaging.

X-rays are usually the first-line imaging test doctors use to look for signs of ankylosing spondylitis. X-rays can reveal inflammation and spinal fusing that are typical of the disease. However, X-rays often can’t pick up these changes in the early stages.

Keep reading to learn more about how X-rays are used in the diagnosis of ankylosing spondylitis and what other tests are used.

No single test can be used to diagnose ankylosing spondylitis. Doctors rely on results from a combination of tests such as:

  • a physical exam
  • imaging tests
  • genetic tests
  • blood tests

The first step of diagnosis often begins with your doctor asking you questions about your symptoms, performing a physical exam, and looking at your medical and family history.

If your doctor suspects ankylosing spondylitis, they will likely refer you for imaging to look for signs of the disease.

What X-rays can reveal

X-rays are the gold standard imaging test used to diagnose ankylosing spondylitis. Spinal X-rays can potentially allow your doctor to see inflammation or fusing of your vertebrae. Your doctor may also recommend getting an X-ray of your ribcage or other affected areas.

X-rays may also be able to pick up other characteristic signs of ankylosing spondylitis such as:

  • bone degeneration
  • hardening or thickening of bone
  • new bone growth

How X-rays help to confirm a diagnosis

An ankylosing spondylitis diagnosis is often made when X-rays show inflammation around your sacroiliac joints and at least one of the following is true:

  • you’ve had back pain for at least 3 months, and it doesn’t improve with rest but improves with exercise
  • you lack range of motion in your lower back
  • you can’t expand your chest as far as expected for your demographic

Changes in your spine are often not visible with X-rays in the early stages of the disease. According to the Spondylitis Association of America, it may take 7 to 10 years for these changes to become significant enough to become visible.

X-rays can also help your doctor track the progression of the disease so they can make changes to your treatment if needed.

X-ray images showing ankylosing spondylitis

You can receive an X-ray in the radiology department of a hospital or a clinic that specializes in imaging. An X-ray technologist or radiologist will perform the X-ray. An X-ray generally takes about 15 minutes to perform, and your doctor will usually receive your results within about 2 days.

It’s a good idea to show up for your appointment about 15 minutes early. If you’re having your spine or pelvis X-rayed, you’ll be asked to change into a gown and may be asked to remove your jewelry and other metal objects. It’s important to let the technologist know if you may be pregnant.

In some cases, you may be given a special dye either through a drink, enema, or injection. This dye helps the image show up more clearly.

The person performing the X-ray will tell you how to best position your body. It’s important to stay still during the X-ray to prevent blurriness.

You will likely be able to resume normal activities immediately after the X-ray

X-rays are generally safe, but they can cause side effects for some people.

X-rays create images by exposing your body to a small amount of ionizing radiation. Ionizing radiation is a type of radiation that has enough energy to potentially damage your DNA.

X-rays slightly increase your chances of developing cancer later in life.

Rare side effects from contrast dyes used in X-rays

In rare cases, contrast dyes can cause side effects that range from mild to severe. Mild side effects can include:

Severe side effects can include:

X-rays are the first-line imaging test for ankylosing spondylitis, but other imaging techniques are also used.

Magnetic resonance imaging (MRI) is more sensitive to detecting inflammation and can sometimes show changes that are undetectable with X-rays. The drawbacks of MRIs are they’re more expensive and generally take longer.

Computed tomography (CT) scans can show some type of changes better than MRIs or X-rays such as joint erosion, thickening of the bone, or fusion of bones.

Along with imaging tests, your doctor may order you a blood test to look for signs of inflammation and rule out other conditions. About 50 to 70 percent of people with ankylosing spondylitis have elevated levels of substances that indicate inflammation.

Your doctor may also recommend a genetic blood test to see if you have the HLA-B27 gene. This gene is found in about 90 percent of people with ankylosing spondylitis but less than 8 percent of people in the general population.

X-rays are the gold standard imaging test for diagnosing ankylosing spondylitis. Your doctor will likely diagnose you with ankylosing spondylitis if your X-rays show signs of inflammation or fusing of your vertebrae and you also have typical symptoms.

Ankylosing spondylitis often doesn’t show up on an X-ray in the early stages of the disease even if you’re experiencing pain and stiffness. If your X-ray comes back normal and your doctor still suspects ankylosing spondylitis, they may recommend an MRI.