Refer a patient with suspected or confirmed ankylosing spondylitis to a rheumatologist if plain film X-ray shows sacroiliitis meeting the modified New York criteria (bilateral grade 2 to 4 or unilateral grade 3 to 4 sacroiliitis) NICE NG65.
If the plain film X-ray does not show sacroiliitis meeting these criteria, or if an X-ray is not appropriate due to skeletal immaturity, request an unenhanced MRI using an inflammatory back pain protocol, and consider referral if MRI meets the ASAS/OMERACT MRI criteria for axial spondyloarthritis NICE NG65.
Refer urgently (same day) for suspected new-onset inflammatory arthritis, including axial spondyloarthritis, especially if there are signs of active inflammation or extra-articular features such as uveitis or psoriasis NICE NG65.
Consider referral if there are frequent flare episodes indicating uncontrolled disease, or if there is a significant change in symptoms suggesting disease progression or complications NICE CKS.