Ankylosing spondylitis (AS) is a progressive inflammatory condition that causes inflammation in the spine and nearby joints in the pelvis. Over a period of time, this inflammation can cause the vertebrae in the spine to fuse, making it less flexible.

While AS mainly affects the spine and vertebrae where tendons and ligaments connect to the bone, it can also affect other joints, including the shoulders, feet, knees, and hips. In rare cases, it can also affect organs and tissue.

There is no single test to diagnose AS, but a full physical exam alongside imaging and laboratory tests may help rule out other possible causes of AS symptoms.

This article covers:

  • methods used to diagnose AS
  • what to expect before an appointment
  • what treatment options are available

There is not a single test to diagnose AS so a doctor must rule out other possible explanations for your symptoms and look for the characteristic cluster of signs and symptoms of AS.

How is AS diagnosed?

A doctor will typically start the process of diagnosing AS with physical tests. Your doctor will also want to get your full medical and family history, as AS can be hereditary.

Your doctor will also ask you:

  • how long you’ve been experiencing symptoms
  • when your symptoms are worse
  • what treatments you’ve tried, what has worked, and what has not
  • what other symptoms you’re experiencing

Compared to other forms of arthritis, one unique characteristic of AS is sacroiliitis. This is inflammation of the sacroiliac joint, where the spine and pelvis connect.

What are signs that I should seek medical attention?

The symptoms and progression of AS will vary between people. Those with the condition will typically experience pain in the lower back, hips, or buttocks. This may develop over the course of several months.

You should see your doctor if your symptoms become severe or keep recurring. Early diagnosis of AS can help to improve overall health outcomes.

Other symptoms may include:

  • stiffness after periods of inactivity
  • swelling in the feet, ribs, shoulders, or neck
  • fatigue
  • appetite loss

Let’s take a look at what you can expect of the tests your doctor may perform to diagnose AS.

A full physical exam

Your doctor conducts a physical exam in order to find telltale signs and symptoms of AS.

Initially, they may look for signs of inflammation and pain in your spine, lower back, and around the pelvis. These are the primary locations of AS symptoms. During this assessment, doctors check if any areas are swollen or tender to the touch.

They may also check your eyes for changes, as AS affects the eyes in around 40 percent of cases, according to Medline Plus.

After looking for signs of inflammation around the lower back, your doctor may passively move your joints or have you do a few exercises so they can observe the range of motion in your joints.

Imaging tests

Imaging tests give your doctor an idea of what’s happening inside your body. The imaging tests you need may include:

  • X-ray. An X-ray allows your doctor to see your joints and bones. They will look for signs of inflammation, damage, or fusion.
  • MRI scan. An MRI sends radio waves and a magnetic field through your body to produce an image of your body’s soft tissues. This helps your doctor see inflammation within and around joints.
  • Ultrasound. Ultrasound scans can play a key role in the early detection and identification of arthritic conditions. These scans use sound waves to map your bones, joints, and tendons.

Laboratory tests

Lab tests your doctor may order include:

  • HLA-B27gene test. Decades of research into AS have revealed one detectable risk factor: your genes. People with the HLA-B27 gene are more susceptible to developing AS. However, not everyone with the gene will develop the disease.
  • Complete blood count (CBC). This test measures the number of red and white blood cells in your body. A CBC test can help identify and rule out other possible conditions.
  • Erythrocyte sedimentation rate (ESR). An ESR test uses a blood sample to measure inflammation in your body.
  • C-reactive protein (CRP). The CRP test also measures inflammation but is more sensitive than an ESR test.

You may first discuss your back pain with your primary care doctor.

If your primary doctor suspects AS, they may refer you to a rheumatologist. This is a type of doctor specializing in arthritis and other conditions that affect the muscles, bones, and joints, including a range of autoimmune diseases.

The rheumatologist is generally the one to accurately diagnose and treat AS.

Because AS is a chronic condition, you may work with your rheumatologist for years. You’ll want to find someone you trust and who has experience with AS.

Doctors’ appointments can sometimes feel stressful and rushed. It’s easy to forget to ask a question or mention a detail about your symptoms.

Here are some things to help you prepare ahead of time that can help you get the most out of your appointment:

  • Make a list of questions you want to ask the doctor.
  • Write out a timeline of your symptoms, including when they started and how they progressed.
  • Gather test results or medical records to show the doctor.
  • Write down anything about your family’s medical history that you think could help the doctor with diagnosis or treatment.

Being prepared will help you make the best use of your time when you see your doctor. Bringing notes can also help relieve the pressure of feeling like you need to remember everything.

There is no cure for AS.

Treatment aims to:

  • relieve your pain
  • preserve your mobility
  • improve your quality of life

To help reduce pain and inflammation, a doctor or rheumatologist may prescribe:

  • nonsteroidal anti-inflammatory drugs (NSAIDS), such as ibuprofen
  • disease-modifying antirheumatic drugs (DMARDs)
  • tumor necrosis factor (TNF) alpha inhibitors
  • steroid injections

Learn more about DMARDs and TNF inhibitors here.

Maintaining your mobility and quality of life are the main considerations of AS treatment. Physical therapy sessions, range of motion exercises, and posture correction can all help you maintain your mobility.

In severe cases, surgery may be recommended to repair joint damage caused by AS.

Learn more about treatments for AS here.