Ankylosing spondylitis (AS) diagnosis can often be a journey, as this condition develops gradually and there isn’t one single, definitive test to identify it immediately. If you suspect you might have AS, consulting your General Practitioner (GP) is the crucial first step. They will start by gathering information about your symptoms, including the nature of your symptoms, when they began, and how long you’ve been experiencing them.
A key indicator that your back pain might be related to AS is its distinctive nature. Unlike typical back pain, AS-related back pain usually doesn’t improve with rest and might even disturb your sleep, waking you up during the night.
Initial Blood Tests and Inflammation Markers
If your GP suspects ankylosing spondylitis, they will likely recommend blood tests to check for signs of inflammation in your body. Inflammation within the spine and joints is a primary characteristic of AS.
Alt text: Blood test being prepared, highlighting the initial diagnostic step for ankylosing spondylitis.
Should the blood test results indicate inflammation, you will typically be referred to a rheumatologist for more specialized evaluation and testing. Rheumatologists are experts in conditions affecting the muscles and joints, making them the ideal specialists for AS diagnosis. It’s important to note that if initial blood tests do not show inflammation, it doesn’t necessarily rule out AS, and further investigation might be needed.
Advanced Tests and Imaging by a Rheumatologist
Upon referral, a rheumatologist will conduct further examinations, including imaging tests to get a detailed view of your spine and pelvis, alongside additional blood tests.
These advanced tests can include:
Genetic Testing for HLA-B27
A genetic blood test may be performed to determine if you carry the HLA-B27 gene variant, which is prevalent in a significant majority of individuals with ankylosing spondylitis.
Alt text: Conceptual image of DNA helix, illustrating the genetic component in ankylosing spondylitis diagnosis through HLA-B27 testing.
While the presence of the HLA-B27 gene can support an AS diagnosis, it is not conclusive. Not everyone with AS has this gene variant, and conversely, some individuals with the gene variant never develop ankylosing spondylitis. Therefore, genetic testing is just one piece of the diagnostic puzzle.
Confirming Ankylosing Spondylitis and Differentiating Axial Spondyloarthritis
Ankylosing spondylitis is categorized as a type of axial spondyloarthritis where inflammation of the sacroiliac joints is visible on an X-ray. However, diagnosing AS can be challenging because spinal inflammation and the fusion of vertebrae (ankylosis) are not always detectable through imaging, especially in the early stages of axial spondyloarthritis. This diagnostic complexity often means that confirming AS can be a lengthy process, sometimes taking several years.
Typically, an AS diagnosis can be confirmed if an X-ray reveals sacroiliitis (inflammation of the sacroiliac joints) and if you also present with at least one of the following criteria:
- Persistent lower back pain lasting for three months or more 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 gender.
If X-ray results are inconclusive for AS, an MRI scan is usually recommended.
Alt text: Medical professional operating an MRI scanner, a crucial imaging technique for ankylosing spondylitis diagnosis when X-rays are inconclusive.
If the MRI scan shows inflammation in the sacroiliac joints, a diagnosis of non-radiographic axial spondyloarthritis will likely be made. This is another form of axial spondyloarthritis. In some instances, inflammation may not be apparent on either X-rays or MRI scans. In such cases, a diagnosis of non-radiographic axial spondyloarthritis might still be considered if you carry the HLA-B27 gene variant and exhibit symptoms consistent with the condition.
Page last reviewed: 05 January 2023
Next review due: 05 January 2026
