There is no direct test for AS
ESR, CRP can be elevated but not sensitive or specific
Xray lumbar/sacroiliac: The earliest changes in the sacroiliac joints shows erosions and sclerosis
Progression of erosions leads to pseudo widening of the joint space and bony ankylosis AKA "Bamboo Spine"
Progression of erosions leads to pseudo widening of the joint space and bony ankylosis AKA "Bamboo Spine"
Often X-ray findings lag about 10 years from initial progression of disease
CBC
Chem 10
Urinalysis
Genetic testing for HLA B27 ( > 90% of people with AS have this gene, though by itself is not specific)
Ankylosing spondylitis
Spine related
Osteoarthritis
Acute ligamentous injury
Rheumatoid arthritis
Acute muscle strain
Reactive arthritis
Disk herniation 