The INCA^TM (Inhaler Compliance Assessment^TM): A comparison with established measures of adherence^†

Objective: To compare the Inhaler Compliance Assessment^TM (INCA^TM), a novel audio-recording device objectively measuring timing and proficiency of inhaler use, against established adherence measures, and explore its discriminant and predictive validity. Design: Prospective observational study; 184 chronic obstructive pulmonary disease (COPD) patients used an INCA^TM-enabled salmeterol/fluticasone inhaler for one-month post-hospital discharge. Main outcome measures: INCA^TM (Attempted, Attempted Interval, Actual) adherence correlated with Doses Used Rate, self-reported adherence and prescription refill for concurrent validity. Discriminant validity for reason for admission, cognition and lung function; predictive validity for health status and quality-of-life. Results: Rates of Attempted, Attempted Interval and Actual adherence were 59, 47 and 23%, respectively. Only 7% of participants had Actual adherence >80%. INCA^TM variables significantly correlated with Doses Used Rate but not with self-report; Attempted and Attempted Interval were weakly associated with prescription refill. Higher cognitive and lung functioning groups had better INCA^TM adherence. Attempted and Attempted Interval predicted health status, while Doses Used Rate predicted quality-of-life. Conclusion: INCA^TM did not strongly correlate with self-report or prescription refill data. Discriminant and predictive validity demonstrated by INCA^TM suggests the potential utility of the INCA^TM as a method to identify intentional and unintentional adherence to inhaled medication and facilitate targeted intervention.