Measurement of utility in asthma: evidence indicating that generic instruments may miss clinically important changes

Accurate assessment of preference-based health-related quality of life is important in determining the value of asthma interventions.

To examine the sensitivity and responsiveness of the EQ-5D and the AQL-5D to differences in asthma control measured by the Asthma Control Questionnaire (ACQ-5).

The Observational Study of Asthma Control and Outcomes was a prospective survey of persistent asthma patients ≥12 years old in Kaiser Colorado. Patients received a survey three times in 1 year, including the ACQ-5, AQL-5D and EQ-5D-3L (including VAS). Censored Least Absolute Deviations (CLAD) and logistic regression were used, controlling for sociodemographics and smoking.

There were 6666 completed surveys (1799 individuals completed all three survey waves). After controlling for covariates, each one-point increase in ACQ-5 was associated with a decrease of 0.066, 0.058, 0.074 and 6.12 in EQ-5D(US), EQ-5D(UK), AQL-5D and VAS scores. Uncontrolled asthma (ACQ-5 > 1.5) was associated with a decrease of 0.15, 0.17, 0.11 and 10, respectively (vs. ACQ ≤ 1.5). AQL-5D scores were statistically significantly different across categories of ACQ-5 scores of 0.5 (the minimum clinically important difference [MCID]), while EQ-5D scores were not significant across most categories. The AQL-5D appeared more robust to changes in control over time (responsiveness) compared to EQ-5D-3L.

The AQL-5D appears more responsive to changes in asthma control over time and more sensitive to detecting differences corresponding to the ACQ-5 MCID than the EQ-5D-3L. Using the EQ-5D-3L without an asthma-specific measure such as the AQL-5D may miss clinically important changes in asthma control.