Validity of bronchiolitis outcome measures

Abstract

Background: The Respiratory Distress Assessment Instrument (RDAI) and Respiratory Assessment Change Score (RACS) are frequently used in bronchiolitis clinical trials, but evidence is limited on their measurement properties. We investigated their validity, reliability, and responsiveness.

Methods: We included data from up to 1765 infants with bronchiolitis enrolled in 2 studies conducted in pediatric emergency departments. We assessed RDAI construct validity by testing hypotheses of associations with physiologic measures (respiratory rate, oxygen saturation) and with constructs related to hospitalization, using correlation coefficients, and multivariable analysis. RDAI/RACS responsiveness was evaluated by using anchors of change based on these constructs; measures of responsiveness included the area under the curve. RDAI test-retest agreement and interrater reliability were evaluated by using limits of agreement and intraclass correlation coefficients.

Results: Baseline RDAI scores were weakly correlated with respiratory rate (r = 0.38, P < .001), and scores increased in lower oxygen saturation categories (P < .001). Higher RDAI scores were associated with hospitalization (odds ratio: 1.36; 95% confidence interval: 1.26-1.47); scores differed between participants who were discharged, admitted, or stayed in the emergency department (P < .001). Our hypotheses were met, but the magnitude of associations was below our predefined thresholds. RDAI test-retest limits of agreement were -3.80 to 3.64 (20% of the range), whereas interrater reliability was good (intraclass correlation coefficient = 0.93). Formulated hypotheses for responsiveness were confirmed, with moderate responsiveness (area under the curve: RDAI, 0.64-0.70; RACS, 0.72).

Conclusions: RDAI has poor to moderate construct validity, with good discriminative properties but considerable test-retest measurement error. The RDAI and RACS are responsive measures of respiratory distress in bronchiolitis but do not encompass all determinants of disease severity.