How good is the agreement between clinical diagnoses and classification criteria fulfilment in axial spondyloarthritis? Results from the SPARTAKUS cohort.

We found an overall good concordance between clinical axSpA diagnoses and classification criteria fulfilment, with 83% fulfilling ASAS axSpA and/or mNY criteria. Regarding axSpA subtypes, the concordance was weaker, and although the ICD-10 code for AS correctly identified patients meeting mNY criteria in 71% of cases, one-third of mNY-positive patients lacked an AS diagnosis. Moreover, clinical u-axSpA diagnoses could not serve as a proxy to identify nr-axSpA, highlighting the importance of thorough classification in research on axSpA subtypes.