Assessing adherence to medications: Is there a difference between a subjective method and an objective method, or between using them concurrently?

BACKGROUND: Patients’ adherence to medication can be assessed by several subjective or objective methods. The Global Initiative for Asthma (GINA) has recommended the use of both measures simultaneously. OBJECTIVE: To assess patients’ adherence to medication using a subjective or an objective method separately, and via using a combination of both methods. As well as identifying the degree of agreement between the two methods. METHODS: Participants who met the study inclusion criteria completed the Adherence to Asthma Medication Questionnaire (AAMQ). A retrospective audit was conducted in order to extract pharmacy refill records for the previous twelve months. The patients’ pharmacy refill records were expressed using the Medication Possession Ratio (MPR). Data were analyzed using the Statistical Package for Social Science. The degree of agreement was determined by Cohen’s kappa coefficient (κ). RESULTS: In terms of the difference in the ability of each method to identify non-adherent patients, a higher percentage of non-adherent patients were identified using the self-reported AAMQ (61.4%) compared to the pharmacy refill records (34.3%). When both methods, in combination, were used to assess adherence, the percentage of non-adherent patients was 80.0%, which is higher than each method when used separately. Twenty percent of the patients were considered adherent on both assessment methods, while 15.7% were considered non-adherent via both methods. Consequently, the AAMQ and pharmacy refill records agreed on 35.7% of the patients. The degree of agreement analysis showed a low correlation between the two methods. CONCLUSION: The combination strategy resulted in a higher percentage of non-adherent patients, compared to using a subjective (the AAMQ) or an objective (the pharmacy refill records) method. The GINA guideline proposition may be supported by the present study’s findings.