The INCA (Inhaler Compliance Assessment): A comparison with established measures of adherence.

Objective: To compare the Inhaler Compliance Assessment (INCA), 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-enabled salmeterol/fluticasone inhaler for one-month post-hospital discharge.

Main Outcome Measures: INCA (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 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 adherence. Attempted and Attempted Interval predicted health status, while Doses Used Rate predicted quality-of-life.

Conclusion: INCA did not strongly correlate with self-report or prescription refill data. Discriminant and predictive validity demonstrated by INCA suggests the potential utility of the INCA as a method to identify intentional and unintentional adherence to inhaled medication and facilitate targeted intervention.