Validity of Medication Adherence Self-Reports in Adults With Type 2 Diabetes

OBJECTIVE To assess the validity of self-report measures of diabetes medication adherence and evaluate the effect of depression on the validity of these reports. RESEARCH DESIGN AND METHODS Adults with type 2 diabetes, treated with oral medications, completed a set of medication adherence self-reports that varied response scales and time frames, were administered structured clinical interviews for depression, and provided blood samples for HbA(1c) as part of a screening for an intervention study. A subsample of participants with HbA(1c) ≥7.0% and clinically significant depression received Medication Event Monitoring System (MEMS) bottle caps to record adherence. Analyses examined relationships between adherence measures and HbA(1c) and, in the subsample, MEMS. Moderated linear regression evaluated whether depression severity modified relationships with HbA(1c). RESULTS Participant (n = 170, 57% men, 81% white, mean HbA(1c) 8.3% [SD, 1.7]) adherence self-reports were significantly (r = -0.18 to -0.28; P < 0.03) associated with lower HbA(1c). In the subsample (n = 88), all self-reports were significantly (r = 0.35 to 0.55; P ≤ 0.001) associated with MEMS-measured adherence. Depression significantly moderated the relationship between three of six self-reports and HbA(1c); at high levels of depression, associations with HbA(1c) became nonsignificant. CONCLUSIONS Results support the validity of easily administered self-reports for diabetes medication adherence. One-month, percentage-based ratings of adherence had the strongest associations with MEMS and HbA(1c); those requiring the report of missed doses had weaker associations. One-week self-ratings and measures that require respondents to record the number of missed doses appear to be vulnerable to bias from depression severity.