Along with showing general symptoms of AS, these characteristics below, combined, are generally used in diagnosis:
- Grade 2 bilateral sacroiliitis OR, Grade 3 or higher unilateral sacroiliitis via Xray - in layman's term this means the signs of damage caused by inflammation of sacral joints (sacroiliitis) seen in both of the sacral joints, OR a definite vision of damage or complete fusion, seen in at least one sacral joint.
- HLA-B27 gene or family history of AS - 80-95% of people with AS have the HLA-B27 gene. Note having the HLA-B27 gene doesn't meant you will have or get AS. Only 9% of the population have this gene, and only 5% of those develop AS. You can have AS without this gene, or any previous history.
- High levels of C-reactive protein (CRP) and raised erythrocyte sedimentation rates (ESR) - determined by a blood test, these levels indicate inflammation. Not everyone who has AS actually show high levels of inflammation in their blood. This is only seen in 50-70% of people with AS.
If you have any suspicions that you may have AS, please speak to your General Practitioner to get a referral to a Rheumatologist to run the necessary tests.
A description of the sacroiliitis gradings can be found here: http://radiopaedia.org/articles/sacroiliitis-grading