Tests for Axial Spondyloarthritis
Reviewed by: HU Medical Review Board | Last reviewed: December 2022 | Last updated: April 2023
There are several types of tests used to diagnose or rule out axial spondyloarthritis (axSpA). They include a detailed physical exam and health history as well as various imaging tests and blood tests. Some of these tests are also used to monitor progression of the condition.1
Physical exam and health history
During your physical exam, your doctor will take your vital signs and look at any areas of concern on your body. During your health history, your doctor will ask about your current and past symptoms. They also may ask about your family history and your habits.1
People with axSpA usually have lower back pain and stiffness for at least 3 months. This usually starts when they are between their teen years and 30s. Men and women may feel this pain differently or in different places. For this reason, it sometimes takes longer for women to be diagnosed with axSpA than men.1,2
Your doctor will also ask if you have, or have had, symptoms of axSpA other than pain. These might include eye swelling (uveitis) or gastrointestinal problems such as inflammatory bowel disease (IBD). They will also want to know about any family history of inflammatory arthritis.1
Imaging tests are medical tests that help doctors see inside the body. Test results can give doctors information about specific parts of the body.3
An X-ray can show changes in the joints that occur in axSpA. One example is inflammation in the sacroiliac (SI) joints, which are located between the base of the spine and the pelvis. This inflammation is called sacroiliitis.3
In radiographic axSpA (r-axSpA), this inflammation is visible on X-ray. R-axSpA is more commonly known as ankylosing spondylitis, or AS.3
A diagnosis of AS can be made if certain features are seen on X-rays, such as evidence of SI joint involvement. X-rays also can show other changes that sometimes occur with axSpA, like:3
- Joints that have grown together (fused)
- Extra, abnormal bone growths (bone spurs)
X-rays do not usually detect early stages of axSpA or mild inflammatory changes.2,3
Magnetic resonance imaging (MRI) machines use strong magnets and radio waves to take pictures of what is going on inside the body. MRI is more sensitive than X-ray. This means it can often find a problem sooner. It may be able to detect the early stages of AS.2,3
MRI can be used to look at inflammation or joint damage in the spine or other joints. It can look at soft tissues and see if there is any inflammation in the joints or entheses. The entheses are the places where ligaments and tendons attach to bones. Inflammation here is called enthesitis.2,3
Computed tomography (CT) uses special X-rays to create cross-sectional images of the body. While CT scans are not usually used to diagnose AS, they can provide more information than regular X-rays.2,3
Ultrasound is a type of imaging that uses sound waves instead of radiation. It creates pictures by bouncing sounds off tissues and organs in the body. Doctors often use ultrasound to look for enthesitis or soft tissue inflammation in people with axSpA.3
Lab tests measure different things in the blood, urine, or other fluids. They can help doctors diagnose axSpA and understand how active it is.2
HLA-B27 antigen blood test
This blood test checks for a protein (genetic marker) called HLA-B27. Research has shown that HLA-B27 is linked to axSpA.2,4
Not everyone with the HLA-B27 genetic marker develops axSpA. Also, many people in the general population have the marker but never go on to develop axSpA. Some people with axSpA never test positive for HLA-B27.2,4
Inflammatory markers blood tests
Inflammatory markers are certain proteins that show up in blood tests when there is increased inflammation in the body. Inflammatory markers that are commonly tested when diagnosing axSpA include:2,5,6
- Erythrocyte sedimentation rate (ESR) – This test measures the rate at which red blood cells settle to the bottom of a tube. A high ESR points to an increase in inflammation. Your doctor may call this a “sed rate.”
- C-reactive protein (CRP) – CRP is a protein made by the liver. It increases when there is increased inflammation in the body. Injury, infection, or inflammatory conditions can raise CRP levels.
Complete blood count (CBC) test
A CBC is a lab test that measures the number of red and white blood cells and other parts of your blood. It can be used to check for signs of an underlying problem.7
A low red blood cell count is known as anemia. This can be a symptom of axSpA. Anemia of chronic disease (ACD) is a type of anemia that can occur with chronic inflammatory conditions such as axSpA.2,7,8
ACD occurs when there are not enough red blood cells produced by the bone marrow. This usually happens gradually. Most cases of ACD are mild to moderate, but symptoms may negatively affect your quality of life.8
Symptoms of ACD include:8
- Shortness of breath
- Pale skin
- Irregular heartbeat
On the other hand, a high white blood cell count may indicate inflammation, infection, or other issues in the body.2,7
Other lab tests
Your doctor will want to rule out other conditions that can cause symptoms similar to axSpA. These conditions include rheumatoid arthritis (RA), gout, and lupus. You might need additional lab tests to help your doctor rule them out, including:9-13
- Rheumatoid factor (RF) – RF is an antibody that often shows up in people with RA. RF is made when the immune system mistakenly attacks healthy tissues, such as joints.
- Uric acid – People with gout have more of this acid. A buildup of uric acid in the body can lead to painful joint problems.
- Antinuclear antibody (ANA) – These antibodies are commonly found in people with lupus and some people with RA, scleroderma, Sjogren’s syndrome, or other conditions. The ANA test looks for harmful antibodies in the blood that can cause inflammation and tissue damage.
- Anti-cyclic citrullinated peptide (anti-CCP) – This antibody test can help doctors tell the difference between types of arthritis and give a more accurate diagnosis.
- Lyme serology – This test is used to detect Lyme disease. Lyme disease can cause inflammation and pain in the joints.