Validação psicométrica de um instrumento para avaliação da adesão à farmacoterapia com varfarina

Abstract

Adherence to warfarin pharmacotherapy remains a significant challenge for health care services, as failures in treatment management may lead to hemorrhagic or thromboembolic events, compromising therapeutic effectiveness and patient safety. In this context, valid and reliable instruments are essential to identify barriers to adherence and to support clinical decision-making. However, most available measures predominantly assess medication intake and fail to comprehensively capture other essential aspects of anticoagulant therapy. This study aimed to perform the psychometric validation of the Instrument for Assessing Adherence to Warfarin Therapy, developed based on a multidimensional conceptual model that encompasses not only medication use but also self-care behaviors and health care follow-up related to anticoagulant therapy. This methodological study was conducted at the Anticoagulation Clinic of Hospital Risoleta Tolentino Neves, in Belo Horizonte, Brazil. A total of 210 patients receiving warfarin participated in the study, of whom 63 completed the retest four to eight weeks after the first instrument administration. Psychometric properties of reliability (internal consistency and temporal stability) and validity (structural and convergent) were evaluated. The internal structure of the instrument was examined using exploratory factor analysis (EFA). Internal consistency was assessed using Cronbach’s alpha, and temporal stability was evaluated using the intraclass correlation coefficient (ICC). Convergent validity was analyzed by correlating the total adherence score with Time in Therapeutic Range (TTR), calculated using the Rosendaal method. The instrument demonstrated excellent sample adequacy, as assessed by the Kaiser–Meyer–Olkin (KMO = 0.98; Bartlett’s test, p < 0.001), high internal consistency (α = 0.98), and excellent temporal stability (ICC = 0.96). A strong positive correlation was observed between the adherence score and TTR (ρ = 0.91), confirming convergent validity. These findings indicate that the instrument is valid, reliable, and clinically applicable, representing a comprehensive tool for assessing adherence to warfarin therapy and contributing to improved quality of care and patient safety.