Validation of the Adherence Barriers Questionnaire – an instrument for identifying potential risk factors associated with medication-related non-adherence

BACKGROUND Medication non-adherence is a major challenge in the real-life treatment of chronically ill patients. To meet this challenge, adherence interventions with a tailored approach towards patient-specific adherence barriers that are identified with a reliable and practicable questionnaire are needed. The aim of this investigation was to develop and validate such a questionnaire, the "Adherence Barriers Questionnaire (ABQ)". METHODS The German ABQ was developed and tested in 432 patients with atrial fibrillation in a multicentre observational cohort study. Evaluation of the questionnaire included an assessment of internal consistency as well as factor analysis. Criterion-related external validity was assessed by comparing the ABQ score with (1) the degree of self-reported adherence and (2) the time in therapeutic range which describes the anticoagulation quality achieved by patients treated with oral anticoagulation. RESULTS The final 14-item ABQ scale demonstrated high internal consistency (Cronbach's alpha = 0.820). Factor analysis identified a three-factor solution, representing intentional adherence barriers with 5 items (31.9% of the variance), medication-/health care system-related adherence barriers with 5 items (13.3% of the variance) and unintentional adherence barriers with 4 items (7.7% of the variance). The ABQ correlated significantly with self-reported non-adherence (Spearman's rho = 0.438, p < 0.001) as well as time in therapeutic range (Spearman's rho = - 0.161, p < 0.010). Patients with above-average ABQ scores (increased number and/or strength of existing adherence barriers) were significantly (p < 0.005, Pearson Chi-Square) more likely to have a poor anticoagulation quality (TTR < 60%) than patients with a lower ABQ score (44.6% versus 27.3%). CONCLUSIONS The ABQ is a practicable, reliable and valid instrument for identifying patient-specific barriers to medication-related adherence. Future research is required to examine the ability of the ABQ to identify patient perception/behaviour changes over time which may be important for the measurement of success of adherence interventions.