Construct Validity of the Routine Assessment of Patient Index Data 3 (RAPID3) in the Evaluation of Axial Spondyloarthritis.

Objective: Although there are different tools to evaluate axial spondyloarthritis (axSpA), they are hardly used in routine clinical practice due to time constraints. The Routine Assessment of Patient Index Data 3 (RAPID3) is a composite measure feasible for use as a sole metric in busy clinics. We aimed to test its measurement properties in patients with axial SpA in a real-world clinical setting.

Methods: This cross-sectional study included 131 consecutive patients with axial SpA. The convergent (Spearman ρ) and discriminant (receiver-operating characteristic [ROC] curve analysis) validity of RAPID3 were tested against several axSpA-specific measures (Bath Ankylosing Spondylitis Disease Activity Index [BASDAI], Ankylosing Spondylitis Disease Activity Score [ASDAS], Bath Ankylosing Spondylitis Functional Index [BASFI], and modified Stoke Ankylosing Spondylitis Spinal Score [mSASSS]). A multivariate model was built to detect disease factors associated with RAPID3 remission (values ≤ 3).

Results: The study included 82 men and 49 women, with a median age of 55 (IQR 46-61) years, and a median disease duration of 11 (IQR 6-24) years. Mean RAPID3 was 9.45 ± 6.7. The BASDAI showed moderate correlation with ASDAS (ρ 0.66, < 0.0001), but higher correlations with BASFI (ρ 0.78, < 0.0001) and RAPID3 (ρ 0.75, < 0.0001). The ASDAS had moderate correlations with BASFI, BASDAI, and RAPID3 (ranges 0.66-0.68, < 0.0001). Higher correlations were found between BASFI and BASDAI (ρ 0.78, < 0.0001), and BASFI and RAPID3 (ρ 0.73, < 0.0001). The mSASSS did not show any correlation with any of the above composite measures. κ agreement between RAPID3 remission and other SpA remission criteria was moderate (κ 0.46-0.56). The RAPID3 thresholds to define remission ranged from values ≤ 2 to ≤ 6 with areas under the ROC curve between 0.86-0.91. Female sex (OR 0.34, 95% CI 0.12-0.90, = 0.03) and nonsteroidal antiinflammatory drug intake (OR 0.26, 95% CI 0.10-0.66, = 0.005) were independently associated with lower odds of achieving RAPID3 remission.

Conclusion: RAPID3 demonstrated construct validity in this cross-sectional study. This index can be useful for a more comprehensive assessment of axSpA in busy clinical settings.