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, P < 0.0001), but higher correlations with BASFI (ρ 0.78, P < 0.0001) and RAPID3 (ρ 0.75, P < 0.0001). The ASDAS had moderate correlations with BASFI, BASDAI, and RAPID3 (ranges 0.66-0.68, P < 0.0001). Higher correlations were found between BASFI and BASDAI (ρ 0.78, P < 0.0001), and BASFI and RAPID3 (ρ 0.73, P < 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, P = 0.03) and nonsteroidal antiinflammatory drug intake (OR 0.26, 95% CI 0.10-0.66, P = 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.