Validation of the inhaler adherence questionnaire.

BACKGROUND

Although electronic monitoring is the "gold standard" for adherence monitoring, the range of inhaler devices on the market exceeds the availability of appropriate monitoring devices. Simple tools, applicable across a range of inhalers, are needed to assess patients' adherence to prescribed inhaled medication. This study reports on the validation of an Inhaler Adherence Questionnaire (IAQ).

METHODS

Seventy-four adults who self-reported doctor diagnosed asthma and who were prescribed daily inhaled corticosteroids (ICS) for asthma contributed data for these analyses. These participants were part of a larger study, investigating factors associated with non-adherence to prescribed daily inhaled corticosteroid medication. Participants were informed the research was investigating asthma management without explicit mention that medication adherence was being monitored. Inhaled corticosteroid medication adherence was measured in two ways. Firstly, participants completed the 6-item IAQ at enrolment. Secondly, ICS via pressurised Metered Dose Inhaler (pMDI) use was monitored electronically using the DoserCT which recorded daily use over 6 weeks. During the 6 weeks of prospective medication monitoring via the DoserCT we did not have contact with participants so that the adherence measure would reflect usual self-management behaviour.

RESULTS

Two of the six questions in the IAQ had poor face validity and their exclusion from the questionnaire resulted in improved internal consistency. Mean days adherent were 37.1, 29.2 and 33.2% for subjects with IAQ scores of 0, 1 and 2 respectively. Higher IAQ scores of 3 and 4 were associated with greater mean days adherent of 73.7 and 67.4% respectively. A cut-point of 2 or less had a sensitivity of 73% and a specificity of 80% for detecting non-adherence. The area under the ROC curve was 0.764 (p < 0.001).

CONCLUSIONS

The modified 4-item IAQ is simple, quick to complete and useful for measuring adherence with prescribed daily inhaled medication. This validation of the IAQ provides evidence for its utility in research and it will be important to validate this simple, inexpensive tool for use in clinical practice.