A cross-sectional study to evaluate the validity of a novel patient-reported outcome measure of medication adherence in Type 2 Diabetes
Authors: Wells J , El-Husseini A , Jaffar A , Dolgin K , Hubert G , Kayyali R 
Published: March 2021

Abstract

Introduction
The average medication adherence (MA) among patients in developed countries living with a chronic disease is estimated to be roughly 50%.(1) Non-adherence is multi-factorial, owing to socio-economic and clinical factors, as well as arguably the most important factor, patients’ health beliefs and experiences. Patient Reported Outcome Measures (PROMs) are often uni-dimensional in their assessment of drivers of MA. This study has evaluated a novel PROM as part of a wider international research initiative focused on Type 2 Diabetes (T2D) which assesses four key factors of MA referred to as Social (S), Psychological (P), Usage (U) and Rationale (R), in short SPUR®.

Aim
To compare the validity of SPUR® against previously validated PROMs in patients with T2D.

Methods
This South London cross-sectional study surveyed adult participants with a confirmed diagnosis of T2D prescribed a minimum of one anti-hyperglycaemic medicine. Surveys were administered face-to-face by community pharmacists using a convenience sampling method based on interactions with pharmacy patients. The survey consisted of questions relating to socio-demographic and clinical data, the SPUR® tool and three previously validated PROMs (BeMQ-General®, MARS-10® and BeMQ-Specific®) as comparators to evaluate factors P, U and R respectively. The Medication Possession Ratio (MPR), a measure of a patient’s pill count in a given time period, was used as an objective comparator of adherence. Pearson’s correlation coefficients (r) were calculated to determine the strength of association between the validated PROMs and SPUR®, with T tests used as a measure of significance (p=&lt;0.05) as an evaluation of validity for SPUR®.

Results
The survey response rate was 21.6% (n=149/690). The modal age range for participants was 60–69 years of age (40.1%, n=60). Participants were predominantly educated to degree level (29.5%, n=44), White (48.3%, n=72) and retired (28.9%, n=43). Overall, 47.6% (n=71) of participants identified as female. Body Mass Index (BMI) data were available for 88.6% (n=132) of the sample with 42.4% (n=56/132) reporting a BMI &gt;30. In ascending order, moderate to strong positive correlations were observed between SPUR® and the comparative PROMs for factors P (r=0.464, p=&lt;0.0001), U (r=0.595, p=&lt;0.0001) and R (r=0.719, p=&lt;0.0001), indicating SPUR® to be a reliable measure of those MA factors. When assessing MA objectively, SPUR® demonstrated the strongest correlation (r=0.281, p=&lt;0.0001) to MPR compared with the validated tools, with MARS-10® as the closest comparator (r=0.266, p=0.001). Despite this, SPUR® did not overestimate MA, 83.8% (n=125) of the sample was identified as adherent based on MPR compared to 53% (n=79) with SPUR®. The latter more closely reflecting HbA1c data which identified 55.4% (n=31/56) as adherent.

Conclusion
Study strengths include the implementation of validated PROMs and two objective MA measures; however, the study sample size was limited. SPUR® has demonstrated its validity against validated PROMs whilst predicting adherence levels without exaggeration, which is often attributed to crude objective measures such as MPR.(2) SPUR® may therefore holistically identify the multiple factors linked to non-adherence, thus supporting the design of individualised interventions.. Such interventions are deemed by the World Health Organisation as potentially more impactful than developing new treatments.(1)

References
1. Eduardo Sabaté (WHO/NMH/CCH). Adherence to long-term therapies: policy for action. World Heal Organ. Published online 2001.
2. Long JA, Wang A, Medvedeva EL, et al. Glucose control and medication adherence among veterans with diabetes and serious mental illness: Does collocation of primary care and mental health care matter? Diabetes Care. Published online 2014. doi:10.2337/dc13-0051