ToolsCalculators
ASAS Criteria for Axial Spondyloarthritis (SpA)
Classifies axial spondyloarthritis in patients with chronic back pain.
ASAS Criteria for Axial Spondyloarthritis (SpA)
Chronic back pain >=3 months with age at onset <45 years
Mandatory entry criterion for the whole criteria set.
Sacroiliitis on imaging
Active inflammation on MRI highly suggestive of SpA-associated sacroiliitis, or definite radiographic sacroiliitis per the modified New York criteria.
HLA-B27 positive
Also counts as one of the SpA features toward the imaging arm.
Inflammatory back pain
Arthritis
Enthesitis (heel)
Uveitis (anterior, past or present)
Dactylitis
Psoriasis
Crohn's disease / ulcerative colitis
Good response to NSAIDs
Family history of spondyloarthritis
Elevated CRP (after exclusion of other causes)
ResultDoes not meet criteria
Entry criterion (chronic back pain >=3 months, onset <45 years) not met; criteria are not applicable.
- Entry criterion met
- No
- SpA features present (excluding HLA-B27)
- 0
- Imaging arm (sacroiliitis + >=1 feature, HLA-B27 counts)
- Negative
- Clinical arm (HLA-B27 + >=2 other features)
- Negative
When to use
- Classifying axial spondyloarthritis (including non-radiographic axSpA) in patients with >=3 months of chronic back pain starting before age 45, for research and cohort classification.
- Not intended as a diagnostic checklist for an individual patient in isolation from clinical judgement.
Formula
Entry: chronic back pain >=3 months, age at onset <45 years. Then classify via EITHER the imaging arm (sacroiliitis on imaging + >=1 SpA feature, where HLA-B27 itself counts as a feature) OR the clinical arm (HLA-B27 positive + >=2 OTHER SpA features, excluding HLA-B27). The 11 SpA features are: inflammatory back pain, arthritis, enthesitis (heel), uveitis, dactylitis, psoriasis, Crohn's/colitis, good response to NSAIDs, family history of SpA, HLA-B27, and elevated CRP.
Pearls and pitfalls
- Sensitivity ~83% and specificity ~84% in the ASAS validation cohort.
- HLA-B27 positivity is itself one of the 11 SpA features: a patient with sacroiliitis on imaging plus HLA-B27 positivity alone (no other feature) satisfies the imaging arm. In the clinical arm, HLA-B27 is the mandatory anchor, so >=2 additional (other) features are still required.
- Classification criteria are designed for research/cohort definition, not as a standalone diagnostic tool.