Doctors sometimes find it difficult to make an ankylosing spondylitis diagnosis because there is no specific laboratory test to confirm that a person has it. A doctor may order a blood test to detect the genetic factor HLA-B27; however, even if the result is positive, the presence of HLA-B27 does not always mean that a person has the disorder.

 

The doctor may use other blood tests besides the HLA-B27 test to help rule out other conditions and confirm a suspected diagnosis of ankylosing spondylitis. For example, the doctor may order rheumatoid factor or antinuclear antibody tests to rule out ankylosing spondylitis. Most people who have the condition will have negative results on these tests. If a person's test results are positive, he or she may have some other condition, such as rheumatoid arthritis or lupus.

 

Doctors also may order a blood test to determine the erythrocyte sedimentation rate (sed rate), which is the rate at which red blood cells settle to the bottom of a test tube of blood. A high sed rate often indicates inflammation somewhere in the body. Typically, people with rheumatic diseases, including ankylosing spondylitis, have an elevated sed rate.

 

Ruling Out Other Medical Conditions

Before diagnosing ankylosing spondylitis, the healthcare provider will consider other conditions that share a number of symptoms and rule them out. Some of these conditions include: