Diagnosing ankylosing spondylitis usually involves multiple tests. When doctors order blood tests to diagnose ankylosing spondylitis, an individual is experiencing worsening symptoms in their back and joints. Often, a blood test diagnosis means the doctor is looking for evidence of anything else that could be causing the symptoms. However, blood tests by themselves cannot definitively diagnose ankylosing spondylitis, but when combined with imaging and assessment, they can provide important clues that point to the answers.

Ankylosing Spondylitis Blood Test Diagnosis

Ankylosing spondylitis is arthritis that primarily affects the spine and hips. It can be difficult to diagnose as no single test can provide thorough information for a definitive diagnosis. A combination of diagnostic tests are utilized, including a physical exam, imaging, and blood tests. Doctors are not only looking for results that will point to ankylosing spondylitis, but they are looking for any results that might point away from the spondylitis results that might provide a different explanation for symptoms.

Physical Exam

The diagnostic process will begin with the individual’s medical history, family history, and physical exam. During the exam, the doctor will ask questions to help rule out other conditions:

• How long have symptoms been presenting?
• Do symptoms get better with rest or exercise?
• Are the symptoms getting worse or staying the same?
• Are the symptoms worse at a particular time of day?

The doctor will check for limitations in mobility and palpate tender areas. Many conditions can cause similar symptoms, so the doctor will check to see if the pain or lack of mobility is consistent with ankylosing spondylitis. The feature sign of ankylosing spondylitis is pain and stiffness in the sacroiliac joints. The sacroiliac joints are located in the lower back, where the base of the spine and pelvis meet. The doctor will look at other spinal conditions and symptoms:

• Back pain symptoms caused by – injuries, posture patterns, and/or sleeping positions.
• Lumbar spinal stenosis
• Rheumatoid arthritis
• Psoriatic arthritis
• Diffuse idiopathic skeletal hyperostosis

Family History

• Family history plays a part in diagnosis because of the genetic element of ankylosing spondylitis.
• The HLA-B27 gene corresponds with ankylosing spondylitis; if an individual has it, one of their parents has it.

Imaging

• X-rays often serve as the first step to a diagnosis.
• As the disease progresses, new small bones form between the vertebrae, eventually fusing them.
• X-rays work best at mapping the disease progression than the initial diagnosis.
• An MRI provides clearer images in the early stages as smaller details are visible.

Blood Tests

Blood tests can help rule out other conditions and check for signs of inflammation, providing supportive evidence along with the results of imaging tests. It typically only takes about a day or two to get the results. The doctor may order one of the following blood tests:

HLA-B27

HLA-B27 test.

• The HLA-B27 gene reveals a red flag that ankylosing spondylitis could be present.
• Individuals with this gene have a much higher risk of developing the condition.
• Combined with symptoms, other labs, and tests, it can help confirm a diagnosis.

ESR

Erythrocyte sedimentation rate or ESR test.

• An ESR test measures inflammation in the body by calculating the rate or how fast red blood cells settle to the bottom of a blood sample.
• If they settle faster than normal, the result is elevated ESR.
• That means the body is experiencing inflammation.
• ESR results may come back high, but these alone do not diagnose AS.

CRP

C-reactive protein – CRP test.

• A CRP test checks CRP levels, a protein associated with inflammation in the body.
• Elevated CRP levels signal inflammation or infection in the body.
• It is a useful tool for measuring disease progression after diagnosis.
• It often corresponds with changes in the spine shown on X-ray or MRI.
• Only 40-50% of individuals with ankylosing spondylitis experience an increased CRP.

ANA

ANA test

• Antinuclear antibodies, or ANA, go after the proteins in the cell’s nucleus, telling the body its cells are the enemy.
• This activates an immune response that the body fights to eliminate.
• A study determined that ANA is found in 19% of individuals suffering from ankylosing spondylitis and is higher in women than men.
• Combined with other tests, the presence of ANA provides another clue to a diagnosis.

Gut Health

• The gut microbiome plays an important role in triggering the development of ankylosing spondylitis and its treatment.
• Tests to determine the gut’s health can give a doctor a complete picture of what is happening inside the body.
• Blood test diagnoses for ankylosing spondylitis and other inflammatory conditions rely heavily on piecing together different tests alongside clinical exams and imaging.

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Causes, Symptoms, Diagnosis, and Treatment

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References

Cardoneanu, Anca, et al. “Characteristics of the intestinal microbiome in ankylosing spondylitis.” Experimental and therapeutic medicine vol. 22,1 (2021): 676. doi:10.3892/etm.2021.10108

Prohaska, E et al. “Antinukleäre Antikörper bei Spondylitis ankylosans (Morbus Bechterew)” [Antinuclear antibodies in ankylosing spondylitis (author’s transl)]. Wiener klinische Wochenschrift vol. 92,24 (1980): 876-9.

Sheehan, Nicholas J. “The ramifications of HLA-B27.” Journal of the Royal Society of Medicine vol. 97,1 (2004): 10-4. doi:10.1177/014107680409700102

Wenker KJ, Quint JM. Ankylosing Spondylitis. [Updated 2022 Apr 9]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: www.ncbi.nlm.nih.gov/books/NBK470173/

Xu, Yong-Yue, et al. “Role of the gut microbiome in ankylosing spondylitis: an analysis of studies in the literature.” Discovery medicine vol. 22,123 (2016): 361-370.