HLA B27 is a test to detect ankylosing spondylitis in hereditary pattern that is whether it is coming from your father or mother.. In many cases it is negative, so ankylosing spondylitis is assessed by clinically evaluating you and doing basic xray of the spine and looking for inflammatory markers in the blood like esr or crp. Based on that we decide to label a patient is ankylosing spondylitis.

A diagnosis Ankolysing spondolytis does not just depend on HLA B27 alone. It is a combination of factors such as serology and radiology along with clinical assessment will establish a diagnosis of AS. Usually, an MRI of the SI joint will also help in identifying early changes in the sacroiliac joint. X rays take up to years to manifest as findings.