BASDAI cut-off values corresponding to ASDAS cut-off values.

OBJECTIVE: To determine cut-off values of BASDAI that can discriminate the four disease activity states (inactive disease, moderate disease activity, high disease activity and very high disease activity), separated by the validated Ankylosing Spondylitis Disease Activity Score (ASDAS) cut-off values (1.3, 2.1 and 3.5). METHODS: We included 333 patients with axial SpA whose data on BASDAI and ASDAS-CRP were available. Receiver operating characteristic curve analysis was performed to determine the BASDAI cut-off values that best corresponded to ASDAS-CRP cut-off values. The degree of agreement between disease activity states based on the BASDAI and ASDAS-CRP cut-off values was assessed using weighted kappa. RESULTS: Of the total 333 patients, 52 (15.6%), 190 (57.1%), 76 (22.8%) and 15 (4.5%) patients had inactive disease, moderate disease activity, high disease activity and very high disease activity, respectively, according to the ASDAS-CRP. Receiver operating characteristic analyses revealed that the BASDAI values 1.9 [area under the curve (AUC) 0.948; 95% CI 0.922, 0.974], 3.5 (AUC 0.926; 95% CI 0.887, 0.966) and 4.9 (AUC 0.917; 95% CI 0.837, 0.996) best corresponded to the ASDAS-CRP values 1.3, 2.1 and 3.5, respectively. The degree of agreement between disease activity states based on the BASDAI and ASDAS-CRP cut-off values was good (weighted kappa: 0.724, P <0.001). CONCLUSION: The BASDAI values 1.9, 3.5 and 4.9 corresponded to the ASDAS-CRP values 1.3, 2.1 and 3.5, respectively. These cut-off values could be useful in clinical studies and real-world practice for determining disease activity status when ASDAS-CRP is unavailable.