Ankylosing spondylitis is a type of arthritis that primarily affects your spine and hips. It can be difficult to diagnosis because there’s no single test that can provide enough information for a definitive diagnosis.

Doctors use a combination of tests to make an ankylosing spondylitis diagnosis such as a physical exam, imaging tests, and blood tests.

In this article, we’ll go over common tests used to diagnose ankylosing spondylitis.

Your doctor will likely start the diagnostic process by considering your medical history and family history as well as performing a physical exam.

During your exam, your doctor may ask you the following questions to help rule out other conditions:

  • How long have you had symptoms?
  • Do your symptoms get better with rest or exercise?
  • Are your symptoms getting worse or staying the same?
  • Are your symptoms worse at a particular time of day?

Your doctor will check for limitations in your mobility and look for tender areas. Many conditions can cause similar symptoms, so your doctor will check to see if your pain or lack of mobility are consistent with the most typical signs of ankylosing spondylitis.

The hallmark sign of ankylosing spondylitis is pain and stiffness of your sacroiliac joints. Your sacroiliac joints are located in your lower back where the base of your spine and pelvis meet.

Other conditions that your doctor will try to rule out include:

Specific physical tests your doctor may perform include the following:

Chest expansion

Ankylosing spondylitis can limit your ability to breathe in fully if your mid-spine or ribs are affected. Your doctor will likely check to see if you can expand your chest as much as would be expected for your age and gender.

Schober test

The Schober test is commonly used to test your degree of lumbar flexion when you bend forward. Limited flexion of your lower back is a common sign of ankylosing spondylitis. Lateral flexion is also tested.

During the Schober test, your doctor will draw lines on your lower back and measure the distance between the lines when you bend forward.

Gaenslen test

The Gaenslen test is commonly used to search for pain and inflammation in your sacroiliac joint. During this test, you’ll lie on your back with a knee pulled to your chest and your opposite leg dangling off the table. Your doctor will put pressure on your opposite leg to see if you experience pain in your joint.

Neurological exam

Your doctor will likely also perform a neurological exam to rule out nerve conditions that affect your muscle strength and reflexes. They’ll also review whether you have other symptoms such as poor bladder and bowel function that could indicate a problem such as a herniated disc.

Blood tests can help rule out other conditions and check for signs of inflammation suggestive of ankylosing spondylitis. Blood tests alone can’t provide enough evidence to diagnose ankylosing spondylitis, but they can provide supportive evidence along with the results of imaging tests.

It usually only takes about a day or two to get the results of your blood tests.

Your doctor may order one of the following blood tests:

  • C-reactive protein (CRP) test. A CRP test checks your levels of CRP, which is a protein associated with inflammation in your body.
  • Erythrocyte sedimentation rate (ESR test). A ESR test measures inflammation in your body by calculating the rate that your red blood cells settle to the bottom of a blood sample.
  • Complete blood count (CBC). A CBC checks your red and white blood cell counts. Increased levels of white blood cells or low levels of red blood cells can indicate inflammation associated with ankylosing spondylitis.

A genetic blood test may also be used to see if you carry the HLA-B27 gene. About 7 percent of Americans have this gene, but it’s found in 90 to 95 percent of people with definite ankylosing spondylitis.

Testing positive for this gene doesn’t mean you have ankylosing spondylitis. Only about 5 to 6 percent of people who carry this gene go on to develop ankylosing spondylitis. But if you carry the HLA-B27 gene, your doctor is more likely to expect that you have the condition. This gene is also connected to an eye inflammation condition (uveitis).

Imaging tests can examine commonly affected areas such as your spine and pelvis to look for signs of anklyosing spondylitis such as:

  • joint fusion
  • erosion
  • extra bone formation (syndesmophyte and osteophyte)
  • calcification

X-rays

X-rays are the most commonly used imaging technique. However, changes to your joints aren’t often visible in the early stages of the disease. According to the Spondylitis Association of America, it can take 7 to 10 years for noticeable changes to appear.

MRIs

If your doctor still suspects ankylosing spondylitis even if X-rays come back negative, they may recommend that you undergo magnetic resonance imaging (MRI).

Researchers are still examining whether ultrasounds are useful for diagnosing or monitoring ankylosing spondylitis.

Usually, a diagnosis can be confirmed when X-rays or MRIs show inflammation of your sacroiliac joint and at least one of the following are true:

  • you have limited chest expansion for your demographic
  • you have limited range of motion in your lower back
  • your back pain hasn’t improved within 3 months, it tends to feel better with exercise, and it gets worse with rest

Once you receive a diagnosis for ankylosing spondylitis, you can work with your doctor to develop a treatment plan.

There’s no cure, but a combination of exercise, physiotherapy, and medications can help you manage pain and stiffness and keep your condition from getting worse.

Non-steroidal anti-inflammatory drugs are often the first-line medication. If they don’t control the inflammation, your doctor will recommend other medications such as: