How Ankylosing Spondylitis Is Diagnosed

Your healthcare provider must take a multi-faceted approach

The diagnosis of ankylosing spondylitis (AS) requires good detective work on the part of your healthcare provider, as there is no test that will guarantee a 100% confirmed diagnosis. Rather, a healthcare provider must consider a person's symptoms, physical examination, and imaging tests, and blood work to make the correct diagnosis.

Since the diagnosis of AS is sometimes subtle, some people are not correctly diagnosed for many years.

How to diagnose ankylosing spondylitis
 Verywell / Cindy Chung

Medical History

A person with AS often first sees their primary care healthcare provider or family medical professional with a complaint about pain, usually in the back or upper buttock.

Features of AS include:

  • Age younger than 40
  • Pain persisting for three or more months
  • The pain improves with exercise
  • Pain worsens with rest, especially at night
  • The pain significantly improves after taking a ​non-steroidal anti-inflammatory (NSAID), such as ibuprofen

These are characteristics of inflammatory arthritis (like ankylosing spondylitis), as opposed to the more common mechanical back pain (for example, muscle strain or degenerative disc disease).

Your healthcare provider will also inquire about whole-body symptoms like fatigue or malaise, as these problems often occur with AS.

In ankylosing spondylitis, your immune system attacks healthy joints, especially the spinal and sacroiliac joints.

A family history of AS, or a personal history of gastrointestinal infections, inflammatory bowel disease, uveitis (inflammation of the colored part of your eye), or psoriasis often accompany AS.

If your primary care healthcare provider or family medical professional suspects that you could have AS or other immune-system mediated process, they may refer you to a rheumatologist—a healthcare provider who specializes in joint and autoimmune diseases.

Physical Examination

Diagnosis of the condition requires a full physical exam. During a physical examination for AS, your healthcare provider will:

  • Examine your spine, hip, and sacroiliac joints by pressing on them to check for tenderness
  • Move your joints to assess your range of motion and flexibility
  • Examine the small joints of your hands and feet, and other joints like your elbows, knees, and shoulders, with special attention to deformities, swelling, warmth, or fluid
  • Check your heels for enthesitis
  • Listen to your lungs
  • Perform a skin and scalp check to look for psoriasis

Do not be surprised if your medical professional refers you to an eye healthcare provider (an ophthalmologist) if you are having any eye pain, redness, and/or blurry vision. Uveitis is a possible complication of ankylosing spondylitis.

Do your best to answer questions your healthcare provider asks—but also don't hesitate to ask your own questions! You should know what they are testing, why, what results mean, and the implications of the results.

Ankylosing Spondylitis Healthcare Provider Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

Doctor Discussion Guide Man

Blood Tests

HLA-B27 Blood test

The main blood test for diagnosing ankylosing spondylitis is the HLA-B27 test.

The test can help support a diagnosis of AS, but it doesn't definitively rule in or rule out the condition.

  • HLA-B27 is present in a large percentage of people with a white racial background who have AS.
  • Of those who are positive for the HLA-B27, only a small percent actually get ankylosing spondylitis.
  • In African-Americans with AS, the HLA-B27 is not as common.

Some people have AS but test negative for the gene. And, HLA-B27 is also present in a relatively high percentage in certain other kinds of inflammatory arthritis, like psoriatic arthritis.

If you are having symptoms suggestive of AS, your healthcare provider may test you for HLA-B27 as part of the diagnostic process.

HLA-B27 is a protein that's found on most cells in your body, including white blood cells (your infection-fighting cells). When present, it can cause your white blood cells to attack healthy cells in your body, like those within your spine, neck, or eyes.

Other Blood Tests

Two other blood tests your healthcare provider may order during your diagnostic evaluation include:

One or both of these markers may be elevated when there is active inflammation in the body. However, CRP and ESR are nonspecific blood tests—they can be elevated in a number of different health conditions besides AS, such as in autoimmune diseases or infection.

In addition, ESR and CRP are sometimes normal in AS, especially if the disease is not flaring at the time of the blood draw.

Imaging Tests

X-rays and sometimes magnetic resonance imaging (MRI) of the sacroiliac joints—and sometimes the spine—are generally used during diagnostic evaluation for possible AS.

A problem with imaging tests is that inflammation can take years to show up. MRI is generally better than X-ray at detecting early signs of disease.

Imaging tests are also used to monitor a person's disease progression after they have been diagnosed with AS.

Ankylosing spondylitis can be considered a smaller subset of a larger group of conditions called axial spondyloarthritis. As part of the ankylosing spondylitis diagnosis, your clinician determines whether you have non-radiographic axial spondylitis or radiographic axial spondylitis.

The latter is considered basically the same as ankylosing spondylitis. This distinction is made primarily based on medical imaging (usually MRI).

Differential Diagnosis

Several conditions diseases can cause some of the symptoms and signs of AS, though they may have other features as well. Since there isn't a confirmatory single test for AS, your healthcare provider will consider other possible causes of your symptoms.

Some medical conditions that have some overlapping signs and symptoms of AS include:

  • Osteoarthritis
  • Psoriatic arthritis
  • Reactive arthritis (arthritis in response to an infection )
  • Arthritis related to inflammatory bowel disease
  • Mechanical back pain
  • Vertebral fracture
  • Back pain resulting from metastatic cancer

Ruling out these other possible problems is important since they often require different treatments.

Frequently Asked Questions

What is ankylosing spondylitis?

Ankylosing spondylitis (AS) is a rare inflammatory form of arthritis that primarily affects the spine and large joints. Also known as Bechterew’s disease, it causes progressive joint stiffening and the loss of joint mobility as well as pain, fatigue, and other symptoms. It is a systemic rheumatic disorder, meaning it's an autoimmune autoinflammatory condition that affects the entire body.

What are the signs and symptoms of ankylosing spondylitis?

Early symptoms include pain and stiffness in the lower back and hips that worsen with inactivity and generally improve with exercise. As the disease progresses, there may significant loss of mobility and increasing pain in the spine, hips, shoulders, heels, and neck (as well as the loss of flexion in the chest and rib cage). Severe cases can lead to kyphosis (“hunchback”).

The majority of people with AS develop symptoms before age 40.

What are complications of ankylosing spondylitis?

Roughly 30% of people who have AS experience uveitis, an inflammatory eye condition causing eye redness, pain, and blurring. Severe cases can affect heart rhythm or heart valve function or lead to lung scarring and interstitial lung disease. Pressure on the spine may also cause cauda equina syndrome, affecting bowel and bladder control.

What causes ankylosing spondylitis?

The exact cause is unknown, but autoimmunity is believed to be the underlying mechanism. Even so, no autoantibody specific to AS has been found. Genetics is believed to contribute because 85% of people with the disease have the HLA-B27. protein, which is hereditary. (With that said, the majority of people with the HLA-B27 do not develop AS).

How is ankylosing spondylitis diagnosed?

There are no tests that can diagnose AS. The diagnosis is based on meeting specific diagnostic criteria (including the onset of symptoms before age 40, pain at night, and relief with activity), supported by blood and imaging tests. Other possible causes must be ruled out to render a definitive diagnosis.

How is ankylosing spondylitis treated?

A combination of medications and therapeutic exercise are commonly used to relieve symptoms and slow disease progression. Drug options include painkillers such as nonsteroidal anti-inflammatory drugs (NSAIDs) and COX-2 inhibitors and disease-modifying anti-rheumatic drugs (DMARDs) such as Azulfidine (sulfasalazine), Enbrel (etanercept), Humira (adalimumab), and Cosentyx (secukinumab).

Can ankylosing spondylitis be treated naturally?

Although the evidence supporting the use of natural therapies is generally lacking, some people have reported improvement of symptoms with complementary and alternative therapies such as:

If you are interested in trying this approach, talk to your healthcare provider about whether natural treatments could be an adjunctive therapy for you. Progression of disease would unlikely be halted with these methods alone.


A diagnosis of AS requires a thoughtful analysis of many factors by your healthcare provider. Your medical history and physical examination are key. Blood tests and X-rays can then strengthen the diagnosis. Sometimes, the correct diagnosis is only revealed over time, as more symptoms appear.

Don't hesitate to ask your healthcare provider about any questions pertaining to your diagnosis or personal test results. Taking an active role in your health can only help you.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Colleen Doherty, MD
 Colleen Doherty, MD, is a board-certified internist living with multiple sclerosis.