Most back pain isn’t caused by ankylosing spondylitis (AS). However, the symptoms, especially in the early stages, can be very similar to more common back problems. Because of this, many people put up with the pain for some time before seeking help. When you first see your doctor, there may be little to show whether the problem is ankylosing spondylitis or some other, more common, back problem. Unfortunately, ankylosing spondylitis may even be misdiagnosed at first. Ankylosing spondylitis is normally diagnosed by a rheumatologist.
There's no specific test that will confirm you have ankylosing spondylitis, so diagnosis involves piecing together information from different sources, including:
- the history of your condition (including whether pain and discomfort is waking you during the second half of the night)
- a physical examination
- blood tests, which may show inflammation.
What tests are there for ankylosing spondylitis?
A blood test can sometimes show if there's inflammation in the body. You'll probably have one or more of these tests:
- C-reactive protein (CRP)
- erythrocyte sedimentation rate (ESR)
- plasma viscosity (PV).
These all test for inflammation, so they give similar information. Different laboratories use particular tests. Only 30–40% of people with ankylosing spondylitis have inflammation that can be picked up in a blood test, so in many cases these blood tests will be normal.
Another blood test can confirm whether you have the HLA-B27 gene. Most people with ankylosing spondylitis test positive for HLA-B27, but so do some people who don't have the condition. A positive test may point to AS but it won't confirm the diagnosis.
X-rays sometimes help to confirm the diagnosis, though they generally don't show anything unusual in the early stages. As the condition progresses new bone develops between the vertebrae, which will be visible in x-ray images. However, it may be several years before these signs show up in x-rays. Magnetic resonance imaging (MRI) scans may show changes in the spine or sacroiliac joints at an earlier stage of the disease.
You may need further tests, especially in the early stages. MRI scans may show the typical changes in your spine and at the sacroiliac joints at an earlier stage of the disease and before changes can be identified on x-rays.