Ankylosing spondylitis

Navigating the Diagnostic Landscape of Ankylosing Spondylitis: A Comprehensive Guide

Ankylosing spondylitis (AS) is a chronic, inflammatory autoimmune disease that primarily affects the spine, causing inflammation in the vertebrae and sacroiliac joints. This inflammation can lead to severe, chronic pain and discomfort, and in advanced cases, can cause new bone formation leading to the fusion of the spine, a condition known as ankylosis. AS can also affect other parts of the body, including the eyes, heart, lungs, and more rarely, the hips and shoulders.

Symptoms of AS typically begin in early adulthood and are often mistaken for more common back problems, which can lead to delays in diagnosis and treatment. However, early diagnosis and intervention with appropriate treatment can help manage pain, maintain flexibility, and reduce the risk of severe spinal damage. In this article, we'll look at how AS is diagnosed and how a timely diagnosis can help you take charge of your AS journey and live your best life with this chronic condition.

Challenges in Diagnosing Ankylosing Spondylitis

One of the main challenges to the diagnosis of ankylosing spondylitis is the non-specific nature of its early symptoms. Back pain and stiffness, the most common symptoms of AS, are also common in many other conditions, making it difficult to pinpoint AS as the cause without further testing. Additional challenges include:

  • slow progression of the disease: AS often develops gradually over many years, and early signs can be easily overlooked or dismissed as general discomfort or aging. This can lead to a delay in diagnosis and treatment, potentially allowing the disease to progress.
  • genetic markers are nonspecific: the genetic marker most commonly associated with AS, the HLA-B27 gene, is not present in all patients with the disease. While this gene is found in a significant proportion of those with AS, its absence does not rule out the condition. This can complicate the diagnostic process, as reliance on this marker alone can lead to missed diagnoses.
  • imaging has limitations: Imaging tests such as X-rays and MRIs are often used to confirm a diagnosis of AS, but these too can present challenges. In the early stages of the disease, changes in the spine or other joints may not be visible on these scans. Furthermore, not all patients with AS will show the classic "bamboo spine" often associated with the disease, leading to potential misdiagnosis.

Diagnostic Criteria for Ankylosing Spondylitis

The diagnostic criteria for AS have evolved from a heavy reliance on X-ray findings to a more comprehensive approach that considers clinical symptoms, genetic markers, and advanced imaging techniques. This evolution reflects the growing understanding of AS as a complex and varied disease, requiring a multifaceted approach for accurate diagnosis.

The Role of Patient History and Symptoms

Patient history and symptoms form the foundation of the diagnostic process for AS. They guide the selection of further diagnostic tests and help health care professionals make an accurate diagnosis. Understanding your history and symptoms also aids in developing an effective treatment plan tailored to your specific needs and circumstances.

A comprehensive patient history provides a broad context for understanding your health status. It includes information about your past and present illnesses, surgeries, allergies, medications, and lifestyle habits. This information can provide clues about your potential risk factors and triggers for AS.

Your patient history also includes a family history of diseases, which is crucial in AS as there is a strong genetic component associated with the condition. If a close family member has AS or another autoimmune disease, your risk of developing AS may be higher.

Clinical Assessments

Ankylosing spondylitis requires a multifaceted approach for accurate diagnosis. Clinical assessments for AS encompass a combination of physical examinations, advanced imaging techniques, and specific laboratory tests. Let’s delve into the details of these diagnostic methods.

Physical Examination

During a physical examination for ankylosing spondylitis, a health care provider will typically look for specific signs that may indicate the presence of the disease. 

  • Schober test: One of the key findings of AS is limited spinal mobility. This can be assessed through the Schober test, where the patient’s ability to bend forward is measured. (Source)
  • FABER test: Another important sign is the presence of pain and tenderness at the sacroiliac joints, which are located at the base of the spine where it connects to the pelvis. This is often evaluated through the FABER (Flexion, ABduction, and External Rotation) test. (Source)
  • uveitis: The health care provider may look for signs of uveitis, an eye inflammation that can occur in people with AS. Symptoms of uveitis may include redness, pain, or blurred vision. (Source)
  • enthesitis: Inflammation of the areas where tendons or ligaments attach to bones, known as enthesitis, is another common finding in AS. This can result in tenderness at these sites, such as the heel (Achilles tendinitis) or the chest (costochondritis). (Source)
  • chest expansion: Reduced chest expansion can be a sign of AS, as the disease can cause inflammation and stiffness in the joints of the ribs. (Source)

Imaging in AS Diagnosis

Imaging plays a vital role in the diagnosis of ankylosing spondylitis, especially when the disease is suspected based on clinical symptoms and history but not yet confirmed. The primary imaging modalities used are X-rays and magnetic resonance imaging (MRI).

  • X-rays are often the first line of imaging used in AS diagnosis. They can reveal changes in the sacroiliac joints, which are located in the lower back where the spine meets the pelvis. In the early stages of AS, X-rays may show inflammation and erosion in these joints. As the disease progresses, X-rays can reveal more pronounced changes, such as fusion of the vertebrae, a condition known as "bamboo spine." However, X-rays may not pick up early signs of AS, and a normal X-ray does not rule out the disease. (Source)
  • Magnetic resonance imaging (MRI) is a more sensitive imaging tool than X-rays and can detect early signs of AS that may not be visible on X-rays. MRI can visualize both bone and soft tissues, making it particularly useful for identifying inflammation in the sacroiliac joints and spinal vertebrae. It can also detect bone marrow edema, a buildup of fluid in bone marrow that is associated with reduced bone density. (Source, Source)

Despite the utility of imaging in AS diagnosis, it’s important to note that the results should be interpreted along with clinical findings and patient history. Imaging results alone are not sufficient to diagnose AS, as changes seen on X-rays or MRI can also occur in other conditions. Therefore, a comprehensive approach that includes clinical evaluation, patient history, blood tests, and imaging is essential for accurate diagnosis of AS.

Laboratory Tests and Biomarkers

Laboratory tests and biomarkers also play crucial roles in diagnosing and monitoring ankylosing spondylitis. They provide valuable information about the immune response and inflammation levels, which can help confirm a diagnosis of AS, monitor disease activity, and guide treatment decisions.

  • HLA-B27: This gene is found in a significant proportion of individuals with AS, but it’s not exclusive to the condition. Therefore, its presence can suggest a higher risk of AS, but it’s not definitive proof. To see if you have the HLA-B27 gene, a sample of your blood will be taken to look for the HLA-B27 antigen, a protein found on the surface of certain white blood cells. (Source)
  • C-reactive protein (CRP): Blood levels of this substance produced by the liver increase when there is inflammation in the body. While high CRP levels can indicate the presence of an inflammatory condition like AS, it can also be elevated due to other conditions such as infection or injury. However, studies have shown elevated CRP levels are associated with AS risk. (Source)
  • erythrocyte sedimentation rate (ESR): The ESR measures the rate at which red blood cells, or erythrocytes, settle at the bottom of a test tube in a period of one hour. The test is based on the principle that inflammation in the body can cause an increase in the production of certain proteins, which in turn makes the red blood cells stick together and settle more quickly. As with CRP, ESR is a general measure of inflammation and is not specific to AS. (Source)
  • autoantibodies: Testing for certain autoantibodies — such as antinuclear antibodies (ANA) and rheumatoid factor (RF) — that are associated with autoimmune diseases other than AS may help rule out these other conditions. 

Differential Diagnosis

Differential diagnosis refers to the process that medical professionals use to distinguish a particular disease or condition from others that present with similar clinical features. In the context of AS, this process is crucial due to the overlap of symptoms with other conditions. (Source)

In the early stages, AS often presents with symptoms such as lower back pain and stiffness, which are common to many conditions. Therefore, it’s important to differentiate AS from other forms of arthritis such as rheumatoid arthritis, osteoarthritis, and psoriatic arthritis, as well as non-inflammatory conditions such as herniated discs (slippage of the rubbery material between vertebrae).

Other conditions that need to be considered in the differential diagnosis include inflammatory bowel disease, which can present with joint pain, and certain infections that can cause joint pain and swelling known as reactive arthritis. In rare cases, malignancies such as lymphoma can present with back pain and systemic symptoms similar to AS. (Source, Source)

Advances and Future Directions in AS Diagnosis

Advances in the diagnosis of AS have been significant in recent years, with a shift towards early detection and intervention. This is largely due to the development of advanced imaging techniques, such as MRI, which can detect inflammatory changes in the sacroiliac joints and spine even in the early stages of the disease. This allows for a more accurate diagnosis before the onset of X-ray changes, which were previously relied upon for a definitive diagnosis.

Genetic testing has also become an important tool in diagnosing AS. The discovery of the HLA-B27 gene and its strong association with AS has provided a valuable biomarker. However, not everyone with this gene develops AS, indicating that other genetic and environmental factors are at play. Therefore, research is ongoing to identify additional genetic markers and environmental triggers that could improve diagnostic accuracy and predict disease progression.

Another promising area of research is the study of biomarkers in blood and other body fluids. These could potentially provide a more objective measure of disease activity and response to treatment. For example, certain types of cytokines, proteins that play a key role in the immune response, are found in higher levels in people with AS. Identifying and tracking these biomarkers could aid in early diagnosis and management of this chronic disease.

How WellTheory Can Help

At WellTheory, we understand the intricacies of navigating autoimmunity — many members of our care team have personal experiences with autoimmune conditions. Our approach is personalized and holistic, encompassing all aspects of your well-being. Here’s how we can support you:

  • personalized care for your unique journey: Autoimmunity affects everyone differently. We take into account your symptoms, lifestyle, and goals to create a care plan that’s uniquely yours.
  • daily guidance and collaborative effort: Living with an autoimmune condition requires continuous care and support. Our collaborative approach ensures that you’re an active participant in your care.
  • evidence-based, data-driven care plans: Our strategies are grounded in the latest scientific evidence to ensure you receive the best advice and guidance. 

The Bottom Line

Ankylosing spondylitis can be challenging to diagnose, particularly in the early stages, because its symptoms can be similar to those of other conditions, and there is no single definitive test for AS. Therefore, it often requires a combination of medical history, physical examination, blood tests, and imaging studies to make an accurate diagnosis. The good news is that getting a timely diagnosis can reduce the risk of future health complications and improve your quality of life. 


Berdal, G., Halvorsen, S., van der Heijde, D., Mowe, M., & Dagfinrude, H. (2012). Restrictive pulmonary function is more prevalent in patients with ankylosing spondylitis than in matched population controls and is associated with impaired spinal mobility: A comparative study. Arthritis Research & Therapy, 14, R19.

Gower, T. (n.d.). Enthesitis and PsA. Arthritis Foundation.

Johns Hopkins Medicine. (n.d.). Reactive arthritis.

Mount Sinai. (n.d.). ESR.

Mount Sinai. (n.d.). HLA-B27 antigen.

Ostergaard, M., & Lambert, R. G. (2012). Imaging in ankylosing spondylitis. Therapeutic Advances in Musculoskeletal Disease, 4(4), 301–311.

Physiopedia. (n.d.). FABER test.

Physiopedia. (n.d.). Schober test.

Riis, A., Olesen, J. L. & Thomsen, J. L. (2020). Early differential diagnosis of ankylosing spondylitis among patients with low back pain in primary care. BMC Family Practice, 21, 90.

Roug, I. K., & McCartney, L. B. (2012). Metastatic non-Hodgkin lymphoma presenting as low back pain and radiculopathy: A case report. Journal of Chiropractic Medicine, 11(3), 202–206.

Shaikh S. A. (2007). Ankylosing spondylitis: Recent breakthroughs in diagnosis and treatment. Journal of the Canadian Chiropractic Association, 51(4), 249–260.

Spondylitis Association of America. (n.d.). Iritis or anterior uveitis.

Su, J., Cui, L., Yang, W., Shi, H., Jin, C., Shu, R., Li, H., Zeng, X., Wu, S., & Gao, X. (2019). Baseline high-sensitivity C-reactive protein predicts the risk of incident ankylosing spondylitis: Results of a community-based prospective study. PLOS ONE, 14(2), e0211946.

Wang, D., Hou, Z., Gong, Y., Chen, S., Lin, L., & Xiao, Z. (2017). Bone edema on magnetic resonance imaging is highly associated with low bone mineral density in patients with ankylosing spondylitis. PLOS ONE, 12(12), e0189569.

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