ASAS classification criteria for axial and peripheral SpA, after Rudwaleit, et al8,9,10.
| Axial SpA Criteria8,9 | Peripheral SpA Criteria10 | |
| In patients with ≥ 3 months back pain and age at onset < 45 yrs | In patients with peripheral symptoms ONLY | |
| Sacroiliitis on imaging plus ≥ 1 SpA feature OR | HLA-B27 plus ≥ 2 other SpA features | Arthritis or enthesitis or dactylitis plus |
| SpA features: | ≥ 1 SpA feature: | |
| · Inflammatory back pain (IBP) | · Uveitis | |
| · Arthritis | · Psoriasis | |
| · Enthesitis (heel) | · Crohn disease/colitis | |
| · Uveitis | · Preceding infection | |
| · Dactylitis | · HLA-B27 | |
| · Psoriasis | · Sacroiliitis on imaging | |
| · Crohn disease/colitis | OR | |
| · Good response to NSAID | ≥ 2 other SpA features: | |
| · Family history for SpA | · Arthritis | |
| · HLA-B27 | · Enthesitis | |
| · Elevated CRP | · Dactylitis | |
| · IBP ever | ||
| · Family history for SpA | ||
The Axial SpA criteria have sensitivity of 79.5% and specificity of 83.3% (n = 975). ASAS: Assessment of Spondyloarthritis Society; CRP: C-reactive protein; NSAID: nonsteroidal antiinflammatory drugs; SpA: spondyloarthritis; IBP: inflammatory back pain.