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Currently, there is no single diagnostic test for ankylosing spondylitis (AS). The clinical diagnosis of ankylosing spondylitis can be made based upon a variety of factors including the patient's signs/symptoms, history, and physical examination. Unfortunately, because low back pain is a relatively common symptom that may be associated with a variety of conditions (primarily mechanical) other than AS, several years may pass between the onset of symptoms and a definitive diagnosis of ankylosing spondylitis. Early diagnosis, however, is important since it may prevent the potentially serious consequences that may develop in the more advanced stages of ankylosing sponylitis.

Diagnostic testing for ankylosing spondylitis usually involves:

• Medical History and Physical Examination
• Laboratory Evaluation
• Radiographic Evaluation

Medical History and Physical Examination

The diagnostic work-up of patients with suspected ankylosing spondylitis begins with a complete medical history including information about:

• Patient's description of symptoms
• When the symptoms started
• Quality and duration of the pain
• Duration of stiffness
• Do the symptoms respond to nonsteroidal antiinflammatory medication (NSAIDs)
• Family history of AS or other spondyloarthropathies
• Any limitations on the patient's overall functional ability and quality of life

After taking a complete medical history, the physician will perform a thorough physical examination. Factors that are evaluated during the physical examination include:

• Testing for sites of inflammation (indicated by pain and tenderness) by applying direct pressure to:

  • the length of the back
  • sacroiliac joint
  • pelvis
  • heels

• Signs of inflammation in peripheral joints

• Range of motion in joints
• Restriction of flexion of joints
• Expansion of the chest during breathing
• Signs of extra-articular manifestations of AS such as inflammation of the uvea (anterior uveitis)

The physician will also observe the patient's posture to see if the lumbar spine is losing its curve and flattening out. There may be secondary muscle spasms which cause a limitation of motion, in which case the limitation of motion appears disproportionate to the damage of observable ankylosis.

Laboratory Evaluation

A variety of laboratory studies may provide useful information that, when combined with the total clinical picture, help to confirm the diagnosis of ankylosing spondylitis. Your doctor will obtain a blood sample and submit it to a laboratory that will perform a variety of tests including:

• HLA-B27 gene - approximately 95% of patients with AS are HLA-B27 positive
• Complete blood count (CBC) - reduction of red blood cell count may be indicative of anemia
• C-reactive protein (CRP) - CRP is a general marker for inflammation and about 50% to 70% of patients with AS have increased levels of in their blood
• Erythrocyte sedimentation rate (ESR) - ESR is another general marker for inflammation and about 50% of patients with AS have an abnormal ESR
• Alkaline phosphatase - levels of this enzyme may be elevated in severe disease
• Serum IgA - Levels of this immunoglobulin (antibody) are usually elevated in patients with AS

Positive results from any of these tests are not specifically diagnostic for ankylosing spondylitis since many of these "acute phase reactants" may be elevated in a variety of inflammatory conditions other than ankylosing spondylitis. There is no relationship between AS and presence of rheumatoid factor (RF) or antinuclear antibodies (ANA) in the blood. A positive test for either RF or ANA is suggestive for another underlying disease process - not ankylosing spondylitis.

Radiographic Evaluation

X-Rays