Diagnosing ankylosing spondylitis (AS) can be a complex journey. This is because the condition often progresses gradually, and there isn’t one single, definitive test to immediately confirm its presence. If you suspect you might have AS, seeking medical advice is the crucial first step towards understanding your symptoms and getting the right diagnosis.
Your initial consultation will likely be with your general practitioner (GP). They will begin by thoroughly discussing your symptoms. Expect questions about:
- The specific symptoms you are experiencing.
- When these symptoms first appeared.
- How long you have been experiencing them.
Back pain associated with AS often has distinctive characteristics. Notably, it typically doesn’t improve with rest and might even disturb your sleep during the night.
Blood Tests in AS Diagnosis
If your GP suspects ankylosing spondylitis based on your symptoms, they may order blood tests to look for indicators of inflammation within your body. Inflammation in the spine and joints is a hallmark of AS.
If the blood test results suggest inflammation, you will likely be referred to a rheumatologist. Rheumatologists specialize in conditions affecting the muscles and joints, making them experts in diagnosing and managing AS.
It’s important to note that even if initial blood tests don’t show inflammation, AS cannot be entirely ruled out. Further investigation and tests might still be necessary to reach a definitive medical diagnosis.
Advanced Diagnostic Tests for Ankylosing Spondylitis
A rheumatologist will conduct further examinations, including imaging tests to visualize your spine and pelvis, alongside more specialized blood tests. These advanced tests are crucial for a precise medical diagnosis of AS.
These further tests may include:
Genetic Testing for HLA-B27
A genetic blood test might be performed to determine if you carry the HLA-B27 gene variant. This gene is present in a significant majority of individuals with ankylosing spondylitis.
While the presence of the HLA-B27 gene can support an AS diagnosis, it’s not conclusive on its own. Not everyone with AS carries this gene, and conversely, some individuals with the gene never develop AS. Therefore, genetic testing is used as part of a broader medical diagnosis process, not as a standalone diagnostic tool.
Confirming Ankylosing Spondylitis or Non-Radiographic Axial Spondyloarthritis
Ankylosing spondylitis is classified as a type of axial spondyloarthritis where inflammation of the sacroiliac joints is visible on an X-ray. This visibility on X-ray is a key factor in differentiating AS from other related conditions in medical diagnosis.
Although imaging scans can detect spinal inflammation and the fusion of vertebrae (ankylosis) in some cases, damage to the spine isn’t always apparent in axial spondyloarthritis, especially in the early stages. This diagnostic challenge is why obtaining a medical diagnosis of AS can often be lengthy, sometimes taking years.
A medical diagnosis of AS is typically confirmed if an X-ray reveals inflammation of the sacroiliac joints (sacroiliitis), and you fulfill at least one of the following criteria:
- Experiencing lower back pain for at least 3 months that improves with exercise but not with rest.
- Limited range of motion in your lower back (lumbar spine).
- Restricted chest expansion compared to the expected range for your age and sex.
If X-ray findings are inconclusive for AS, an MRI scan is usually recommended.
If an MRI scan reveals inflammation of the sacroiliac joints, you may be diagnosed with non-radiographic axial spondyloarthritis. This is another form of axial spondyloarthritis, closely related to AS, but where joint damage is not yet visible on X-ray. Medical diagnosis differentiates these conditions through imaging and symptom evaluation.
In situations where inflammation isn’t evident on either X-rays or MRI scans, a medical diagnosis of non-radiographic axial spondyloarthritis might still be made if you carry the HLA-B27 gene and present with symptoms consistent with the condition.
Page last reviewed: 05 January 2023
Next review due: 05 January 2026
