ASAS refers to the assessment of the SpondyloArthritis international Society. Ankylosing spondylitis (AS) is a form of chronic inflammatory arthritis characterized by sacroiliitis, enthesitis, and a marked propensity for sacroiliac joint and spinal fusion. AS is a condition in the spondyloarthritis (SpA) family of disease and distinguished by universal involvement with joint inflammation or fusion, and more prevalent spinal ankylosis. ASAS criteria for axial spondyloarthritis (SpA) can be used for patients who meet entry criteria and required criteria. Entry criteria: patients who have had chronic back pain (for more than equal 3 months) of unknown origin (no definite diagnosis) that began before 45 years of age. Required criteria: Sacroiliitis on imaging (Note) plus ≥1 SpA feature, or HLA-B27 plus ≥2 additional SpA features. SpA features are including: Inflammatory back pain, Arthritis, Enthesitis (heel), Uveitis, Dactylitis, Psoriasis, Crohn’s disease or ulcerative colitis, Good response to NSAIDs, Family history of SpA, HLA-B27, Elevated CRP. Note: Sacroiliitis by radiographs refers to bilateral grade 2–4 or unilateral grade 3–4 sacroiliitis on plain radiographs, according to the modified New York criteria. Sacroiliitis by MRI refers to active (acute) inflammatory lesions of sacroiliac joints with definite bone marrow oedema/osteitis, suggestive of sacroiliitis associated with SpA. ASA classification for axial SpA and Diagnostic result: patient with back pain >=3 months and age <45 years= Yes, Sarcroiliitis on imaging=Yes , Diagnostic result= Not axial SpA patient with back pain >=3 months and age <45 years= Yes, Sarcroiliitis on imaging=Yes, ≥1 SpA features= Yes, Diagnostic result= Axial SpA patient with back pain >=3 months and age <45 years= Yes, HLA-B27=Yes, Diagnostic result= Not axial SpA patient with back pain >=3 months and age <45 years= Yes, HLA-B27=Yes, ≥2 SpA features other than HLA-B27 positive= Yes, Diagnostic result= Axial SpA