Table 1

ASAS criteria for classification of axial spondyloarthritis (SpA) in patients with back pain ≥3 months and age at onset back pain <45 years (with/without peripheral manifestations)109

Sacroiliitis on imaging* plus ≥1 SpA feature**orHLA-B27 plus ≥2 other SpA features**

  • **SpA features

  • –Inflammatory back pain

  • –Arthritis

  • –Enthesitis (heel)

  • –Uveitis

  • –Dactylitis

  • –Psoriasis

  • –Crohn's/ulcerative colitis

  • –Good response to NSAIDs

  • –Family history for SpA

  • –HLA-B27

  • –Elevated CRP

  • *Sacroiliitis on imaging

  • –Active (acute) inflammation on MRI highly suggestive of sacroiliitis associated with SpA

  • –Definite radiographic sacroiliitis according to modified New York criteria

  • ASAS, The Assessment of SpondyloArthritis international Society; CRP, C-reactive protein; NSAIDs, non-steroidal anti-inflammatory drugs.