Sacroiliitis on imaging (MRI or radiography) and ≥1 other feature of SpA

or

Presence of HLA-B27 antigen and ≥2 other features of SpA

Features of SpA:

– Inflammatory back paina

– Peripheral arthritis

– Enthesitis (heel)

– Uveitis

– Dactylitis

– Psoriasis

– Crohn disease or ulcerative colitis

– Good response to NSAIDs (resolution or significant improvement of back pain within 24-48 h of administration of a full dose)

– Family history of SpA

– HLA-B27

– Elevated serum CRP level (when other causes have been excluded)

Arthritis, enthesitis, or dactylitis

and

≥1 of the following features of SpA:

– Anterior uveitis

– Psoriasis

– Crohn disease or ulcerative colitis

– Prior infection

– HLA-B27

– Sacroiliitis on imaging

or

≥2 of the following features of SpA:

– Arthritis

– Enthesitis

– Dactylitis

– Inflammatory back paina (at any time in history)

– Family history of SpA

a Characterized by ≥4 of the following: (1) age of onset <40 years; (2) insidious onset; (3) reduced by exercise; (4) not relieved by rest; (5) present at night (decreases after getting up).