The association between nonadherence and glycated hemoglobin among type 2 diabetes patients using basal insulin analogs

BACKGROUND The main objective of this study was to investigate the relationship between adherence and both clinical (ie, glycated hemoglobin [HbA1c]) and nonclinical (ie, health status, work impairment, and health care-resource use) health outcomes among type 2 diabetes (T2D) patients using basal insulin. MATERIALS AND METHODS The 2012 US National Health and Wellness Survey dataset was used for this study (n=71,141). A total of 1,198 respondents who reported a diagnosis of T2D, were currently using basal insulin, and reported both their HbA1c and level of nonadherence were included in the analyses. Classical test theory and item response theory (IRT) analyses were used to provide evidence for the Morisky Medication Adherence Scale (MMAS) in this population. Adherence was then used as a predictor of HbA1c and nonclinical outcomes using regression modeling, controlling for demographics and health history. RESULTS A total of 61.44% of respondents were male, and the mean age was 60.65 (standard deviation 10.74) years. Internal consistency of the eight-item MMAS (MMAS-8) was adequate (Cronbach's α =0.68), and one factor was retained (eigenvalue =1.80). IRT analyses suggested that the MMAS-8 was most precise for those with high levels of nonadherence. A significant relationship between variables emerged, whereby each point increase in the level of nonadherence was associated with a 0.21 increase in HbA1c (B=0.212, P<0.05). A modest quadratic trend was also observed (B=0.026, P<0.05), indicating that the benefit to HbA1c may taper off at high adherence. Each point of nonadherence was associated with a 4.6%, 20.4%, and 20.9% increase in the number of physician visits, emergency room visits, and hospitalizations, respectively. DISCUSSION This study provides evidence that adherence rates are high among patients with T2D using basal insulin, and the MMAS-8 is a reliable and valid tool to assess adherence. Further, the results suggest that HbA1c increases concomitantly with nonadherence, as do poorer health status and health care-resource use.