A Systematic Review of Insulin Adherence Measures in Patients with Diabetes

Diabetes care is associated with a considerable burden to the health care system in the United States, and measuring the quality of health care is an important development goal of the Department of Health and Human Services and the Centers for Medicare & Medicaid Services. Diabetes is a priority disease within the National Quality Strategy and should therefore remain a focus in the measurement of health care quality. Despite the importance of measuring quality in diabetes care management, no quality measure is currently associated with adherence to insulin treatment, and measuring adherence to insulin is known to be complicated.

To (a) identify methods to measure insulin adherence in patients with diabetes and (b) evaluate whether identified methods could be considered for testing as a quality measure.

Systematic searches were conducted in the online electronic databases Embase, MEDLINE, and the Cochrane Library, supplemented with additional manual searches to identify publications on insulin adherence from the year 2000 onward. Identified citations were screened for relevance against predefined eligibility criteria, and methods to measure adherence to insulin were extracted from relevant studies into data extraction tables. Methods were critiqued on the feasibility for consideration as a quality measure.

Seventy-eight publications met the inclusion criteria and were reviewed. Included studies reported various indirect methods to measure adherence to insulin, using prescription claims or self-report questionnaires. Commonly reported methods included the (adjusted) medication possession ratio, proportion of days covered, persistence, daily average consumption, and the Morisky Medication Adherence Scale. All types of identified methods were associated with measuring challenges varying from accuracy of estimated adherence, complexity of data collection, absence of validated threshold for good adherence, and reliability of adherence outcomes.

Without additional research, none of the identified methods are appropriate for use as a quality measure for insulin adherence. We suggest patient involvement in future research and additional quality measure development.

Novo Nordisk paid DRG Abacus to complete the systematic review and manuscript and was involved in the study design, interpretation of data, and decision to publish the findings of the systematic review. Kroes and Webb report personal fees from Novo Nordisk during the conduct of the study and personal fees from DRG Abacus, outside of the submitted work. Webb is employed by DRG Abacus, and Kroes was employed by DRG Abacus at the time of this study. Wisniewski is an employee of Novo Nordisk, which funded the systematic review reported in this article, and also owns stocks in Novo Nordisk. Stolpe has nothing to disclose. Study concept and design were contributed by Kroes, Webb, and Wisniewski, with assistance from Stolpe. Webb took the lead in data collection, along with Kroes, and data interpretation was performed by all the authors. The manuscript was written by Kroes, Webb, and Wisniewski, with assistance from Stolpe, and revised by Kroes, Stolpe, Wisniewski, and Webb.