What do we mean by adherence to treatment and advice for living with diabetes? A review of the literature on definitions and measurements.

AIMS: In order to measure the effectiveness of interventions claiming to improve adherence in diabetes, valid measurement of adherence is necessary. Any measurement must first be based on a definition. This study aimed to identify and categorize definitions and measurements of adherence in living with diabetes, from a review of the literature.
METHODS: Publications were identified from the medline database. Adherence, compliance and concordance were used as terms in the search algorithm, along with diabetes, diabetes mellitus and treatment. Two hundred and ninety-three papers were identified. Abstracts of these papers were read by two researchers independently. Two hundred and thirty-nine papers did not contain definitions or measures of adherence and were discarded. Of the remaining 54 papers, 26 included definitions and 46 described measurements of adherence.
RESULTS: Definitions and measurements fell into five categories: coincidence of behaviour with professional advice, relationship as part of the process of care, outcome and process targets, taking the medication as prescribed and others. No single definition of adherence emerged. Many authors did not provide definitions of adherence. Glycated haemoglobin was the most common measurement of adherence, although this can raise problems.
CONCLUSIONS: Research which claims to show an intervention has, or has not, improved adherence must be interpreted cautiously. Interventions which appear to fail may actually succeed in aspects of adherence which were not defined or measured in the study. Clinicians and researchers could use clear definitions and measurements, such as the ones presented in this review.