Comparison of Three Adherence Assessment Tools in Omani Patients with Type 2 Diabetes Mellitus: A Single-Center Cross-Sectional Study of Agreement and Association with HbA1c.

Purpose: Discrepancies in adherence classification across assessment tools pose a challenge in clinical practice. This study compared three medication adherence assessment tools-the 8-item Morisky Medication Adherence Scale (MMAS-8), the Single-Item Self-Adherence Assessment (SISA), and the Omani-validated Medication Adherence Universal Questionnaire (MAUQ-ar-OM)-with respect to their agreement, their association with glycated hemoglobin (HbA1c), and their identification of behavioral and belief-related barriers in patients with type 2 diabetes mellitus (T2DM). Patients and Methods: This cross-sectional study was conducted at the endocrinology clinic of a tertiary-care academic hospital in Oman, among Arabic-speaking Omani adults (≥18 years) with T2DM who were receiving oral hypoglycemic agents, either alone or in combination with insulin. Adherence was classified into three levels (high, moderate, and low). In a predefined subgroup of 98 participants, the MAUQ-ar-OM was used to identify adherence barriers across four domains: positive attitudes toward healthcare and medication, lack of discipline, aversion toward medication, and active coping with health problems. Results: A total of 233 patients were included, of whom 50.7% were female. The median age was 58 years and the median HbA1c was 8.8%. Adherence classification varied markedly across tools: high adherence was reported in 88.8% of patients by the SISA versus 46.6% by the MMAS-8. Agreement between MMAS-8 and SISA was slight-to-fair beyond chance (quadratic weighted Cohen's κ = 0.248; p<0.01). Lower MMAS-8 scores were associated with higher HbA1c values (p<0.01). Within the MAUQ-ar-OM, the lack-of-discipline domain emerged as a barrier most closely aligned with adherence behavior (p=0.237, p=0.019). Conclusion: In this cross -sectional study, MMAS-8 showed a stronger association with HbA1c and may help identify patients with poorer glycemic control, whereas SISA offered a rapid assessment but appeared to classify a higher proportion of patients as highly adherent. The MAUQ-ar-OM identified lack of discipline as a potentially modifiable adherence barrier. Because this was a cross-sectional study using self-reported measures, prospective studies incorporating objective adherence measures are needed before concluding that any single tool is superior. A combined approach that integrates a brief screening tool with a comprehensive assessment may warrant further evaluation to optimize diabetes care.