Home Science Genetics Diagnosing Ankylosing Spondylitis: Tests and Exams

Diagnosing Ankylosing Spondylitis: Tests and Exams

Diagnosing Ankylosing Spondylitis: Tests and Exams

If you experience lower back pain that lasts three or more months, you may have some sort of axial spondylitis (axial SpA). ankylosing spondylitis (AS). AS is an aggressive autoimmune disease, so getting an early diagnosis and starting treatment right away is critical.

The tests used to diagnose ankylosing spondylitis include a physical exam, a medical history, blood tests, genetic testing, and imaging.

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Symptoms of AS usually begin in the late teens to mid-thirties, but anyone can get it, including children. But because the symptoms start slowly, they are often ignored or confused with other health problems. Reports from 2015 found that the average diagnostic delay for axial SpA is eight years.

It’s not uncommon for people with AS to see multiple health care providers to manage the back pain and stiffness that manifests AS. These medical professionals may include primary care providers, orthopedists (specialists in musculoskeletal disorders), physical therapists, and chiropractors.

But the type of health care provider best able to diagnose AS is a rheumatologist— a doctor with specialized training in musculoskeletal and autoimmune diseases like. If you have symptoms suggestive of AS, make an appointment with a rheumatologist or ask your primary care provider for a referral.

This article covers tests to diagnose AS, including physical and neurological exams, blood tests, genetic testing, and imaging.

Ankylosing Spondylitis Physical Examination

A physical exam for AS usually begins with a thorough review of your medical and family history.

Your medical history looks at whether your back pain is mechanical or inflammatory. According to the Spondylitis Association of America, mechanical back pain occurs as a result of physical changes in the back. It is often the result of everyday activities such as lifting heavy objects, incorrect posture or poor sleeping position.

On the other hand, inflammatory back pain related to AS is persistent, lasting more than three months, affecting people younger than 35 years of age, and worsening after periods of inactivity. Inflammatory back pain will improve with movement, exercise, and exercise non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen.

In addition to understanding the nature of your back pain, your health care provider will want to know when symptoms started and what makes them worse and better. They also want to learn about systemic symptoms (symptoms that affect the entire body) and other joint pain in the neck, hips, shoulders, arms, and legs.

It is helpful to share every detail about your symptoms and overall health to help the healthcare provider make an accurate diagnosis.

The HLA-B27 gene, which can lead to AS, is inherited. In addition, family and twin studies have shown that AS has a strong genetic component. You should inform your healthcare provider if AS or other autoimmune diseases run in your family.

Once the health care provider has information about your medical and family history, they will want to perform a thorough physical and neurological exam.

During the physical exam, you will be asked to flex your back and hips in different directions to check for stiffness and pain. They may also push on some body parts to look for tender spots.

Since breathing difficulties are a sign of severe AS, the health care provider will also monitor your breathing. Breathing problems in AS result from lung scarring due to inflammation, forward bending of the upper body, and stiffening of the chest wall.

The neurological exam assesses sensory and motor functions, including reflexes and muscle strength. Your healthcare provider will also assess your other neurological symptoms, such as nerve pain, numbness, tingling, muscle weakness or spasms, and bowel and bladder dysfunction.

Blood test for ankylosing spondylitis

Blood tests can look for signs of inflammation suggestive of AS. It is also done to rule out other conditions. Blood tests aren’t enough to confirm AS, but they help the health care provider understand your symptoms.

There are no specific tests to confirm AS, but certain blood tests can check for inflammatory markers and rule out other conditions that cause similar symptoms.

The following blood tests may be ordered if AS is suspected:

  • Erythrocyte sedimentation rate (ESR or sed rate): The ESR test detects inflammation in the body. ESR rate is measured by how fast red blood cells settle in a test tube.
  • C-reactive protein (CRP): CRP is a protein made by the liver. High levels of CRP are an indication of a condition that causes inflammation.
  • Complete blood count (CBC): The CBC test checks the blood cell count. A high white blood cell count and a low red blood cell count indicate inflammation that is often associated with AS.
  • rheumatic factor (RF): RF is often associated with other autoimmune arthritis conditions such as Rheumatoid arthritis and lupus. The RF test is ordered to rule out these conditions when AS is suspected.

Genetic testing for ankylosing spondylitis

A genetic blood test can be requested to see if you are a carrier of the HLA-B27 gene. According to a 2018 report, this gene is only found in 8% of the general population. HLA-B27 is present in 90% of people with AS.

Testing positive for HLA-B27 does not mean you will develop AS. According to a 2019 report, only about 5% to 6% of people with the gene will develop AS report in the journal Bone Research.

If you are a carrier of the HLA-B27 gene, your healthcare provider is more likely to suspect AS. This gene is also linked to more serious AS symptoms, such as eye inflammation and a condition known as uveitis (inflammation of the middle layer of tissue in the eye wall).

Imaging tests for ankylosing spondylitis

Several imaging tests can help diagnose AS, including: conventional radiology (X-rays), magnetic resonance imaging (MRI), computed tomography (CT) and ultrasound. X-rays are standard for diagnosing AS, while a CT, MRI, or ultrasound may be requested to evaluate bone and soft tissues of the spine in more detail.

If your healthcare provider requests imaging, they may be looking for the following signs of AS:

  • sacroiliitis (inflammation of one or both SI joints)
  • Loss of cartilage in the facet joints (located between the vertebrae), which can lead to fusion
  • Loss of normal curvature of the spine, leading to kyphosis (humpback whale) or lordosis (sway back)
  • Spine and pelvic fractures
  • Bone erosion (bone loss) in the low back
  • Bone growth in the vertebrae
  • Calcification (bone hardening)

Your healthcare provider may use X-rays and MRI to monitor the progression of AS disease or to look for fractures or joint damage.

Confirming a diagnosis of ankylosing spondylitis

Your healthcare provider will rely on your physical and neurological exams, symptom history, imaging results, and blood tests to diagnose AS.

According to a 2020 Rheumatology report, a healthcare provider can diagnose AS based on specific criteria, including:

  • Back symptoms: This includes back pain that has lasted for three or months and started before age 40, which resolves with exercise and is worse in the morning and after periods of inactivity, back pain progressing to buttock pain, and limited movement of the lower back
  • Finding relief with NSAIDs, indicating that back pain is due to inflammation
  • peripheral manifestations, such as arthritis in the arms, legs and shoulders, dactylitis (swelling of the fingers and toes), and enthesis (inflammation of the entheses – the places where tendons and ligaments attach to bone)
  • Extra-musculoskeletal manifestations, such as uveitis, psoriasis (a chronic skin condition), and inflammatory bowel disease
  • Positive family history of AS
  • HLA-B27 positivity
  • High CRP and ESR values
  • Evidence of sacroiliitis on imaging
  • Osteitis (bone inflammation) and/or bone marrow edema (fluid build-up in the bone marrow), which can be seen on an MRI

If you have had inflammatory back pain for at least three or more months, along with other features that are part of AS diagnostic criteria, your healthcare provider will likely diagnose you with AS.


Ankylosing spondylitis is an autoimmune disease that occurs when the immune system malfunctions and attacks healthy tissues, primarily the small bones of the spine. AS is an aggressive condition and early diagnosis is crucial for reducing spinal complications, such as spinal fusion, fractures, and abnormal curvatures.

If you experience signs and symptoms of AS, such as pain and stiffness in the lower back and hips, contact a healthcare provider so they can request a test to determine the cause. Tests used to diagnose AS include physical and neurological exams, blood tests, genetic testing, and imaging.

A diagnosis of AS is usually made based on symptoms, blood tests, imaging results, and HLA-B27 positivity.

A word from very good

Ankylosing spondylitis is a lifelong condition. There is no cure for the disease, but it is treatable and manageable.

You will have many options for treating your condition, which can reduce symptoms and prevent disease progression. Taking your medications as prescribed is crucial to slowing down the effects of the disease on you, keeping you moving and independent, and maintaining a good quality of life.

In addition to following your treatment plan, you should see a rheumatologist regularly. And be sure to speak up if your treatment plan isn’t adequately controlling your symptoms.

Frequently Asked Questions

  • What Are the Early Warning Signs of Ankylosing Spondylitis?

    The earliest signs of ankylosing spondylitis are pain and stiffness of the low back and hips, especially in the morning and after periods of inactivity. You may also experience neck pain and fatigue. Over time, these symptoms will worsen or improve during flare-ups (exacerbation of the disease) and remission (no symptoms).

  • Should You See a Specialist for Ankylosing Spondylitis Testing?

    If you experience symptoms of ankylosing spondylitis, a primary care provider may refer you to a rheumatologist. A rheumatologist is specially trained in diagnosing and treating conditions such as AS that affect the joints, muscles, connective tissues, and bones.

  • What happens after receiving an ankylosing spondylitis diagnosis?

    After you’ve been diagnosed with ankylosing spondylitis, you’ll want to work with your healthcare provider to create a treatment plan. You’ll be prescribed medications and given information about lifestyle habits to help manage symptoms, such as dietary changes, exercise, and modification tools to reduce joint stress.



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