Performance of the assessment in Spondyloarthritis International Society classification for axial and peripheral spondyloarthritis in an established clinical cohort: comparison with criteria sets of Amor and the European Spondylarthropathy Study Group.

OBJECTIVE: To evaluate the performance of the Assessment in Spondyloarthritis International Society (ASAS) criteria (axial or peripheral) against the Amor and European Spondylarthropathy Study Group criteria in established spondyloarthritis (SpA).
METHODS: Rheumatologist-diagnosed patients with SpA were retrospectively classified according to the different criteria sets. Clinical characteristics of patients fulfilling all 3 criteria were compared with those who did not, by nonparametric statistics.
RESULTS: ASAS classified 90% of the 231 patients, with 169 (73%) fulfilling all 3 criteria sets. Multivariate analysis showed the 62 patients not fulfilling all criteria sets were older at symptom onset (p < 0.001) and less likely to have inflammatory back pain (p < 0.001), peripheral arthritis (p < 0.001), or elevated C-reactive protein levels (p = 0.034).
CONCLUSION: ASAS criteria can be used in established disease.