Reliability of the Bath Ankylosing Spondylitis Disease Activity Index and the Bath Ankylosing Spondylitis Functional Index administered via tele-assessment in patients with axial spondyloarthritis

Abstract

Introduction: The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Bath Ankylosing Spondylitis Functional Index (BASFI) are widely used to assess disease activity and function in patients with axial spondyloarthritis (axSpA). However, their reliability when administered via tele-assessment has not been investigated. This study aimed to evaluate the reliability of BASDAI and BASFI administered via tele-assessment in axSpA patients. Methods: This study included patients with axSpA. BASDAI and BASFI were administered by phone at two separate times, 24 hours apart (test-retest). Internal consistency was assessed using Cronbach's alpha, and test-retest reliability was evaluated using intraclass correlation coefficients (ICC). Absolute reliability was assessed using the Bland-Altman method, standard error of measurement (SEM), and minimal detectable change (MDC95). Results: The study initially included 110 patients, with 102 completing the study. BASDAI showed adequate internal consistency (Cronbach's alpha = 0.769), and BASFI showed excellent consistency (Cronbach's alpha = 0.879). The test-retest reliability for BASDAI (ICC(3,1) = 0.864, 95% CI = 0.790-0.911) was good and for BASFI (ICC(3,1) = 0.949, 95% CI = 0.925-0.965) was excellent. SEM and MDC95 values for BASDAI were 0.71 and 1.97, respectively, and for BASFI, 0.44 and 1.22. Bland-Altman plots indicated good agreement, with no significant proportional bias. Conclusion: Both BASDAI and BASFI demonstrated good internal consistency and good to excellent test-retest reliability when administered via tele-assessment. These tools can be reliably used for remote monitoring of disease activity and functional status in patients with axSpA.Trial registrationClinicalTrials.gov, NCT06230952, https://clinicaltrials.gov/study/NCT06230952?cond = reliability%20BASDAI&rank = 1.