Development and validation of a tool assessing adherence to warfarin therapy (TAAW) by Brazilian patients

Abstract Aim To develop and validate a multidimensional tool to assess adherence to warfarin therapy by Brazilian patients. Methods A Tool for Assessing Adherence to Warfarin Therapy (TAAW) was designed to encompass warfarin intake and other treatment‐related aspects, including causal and effect items of adherence. The development process included: (i) construction of a concept map; (ii) elaboration of a preliminary version; (iii) expert assessment; (iv) semantic analysis through pre‐testing with 30 participants; and (v) psychometric validation, including exploratory factor analysis, internal consistency, test–retest reliability and hypothesis testing. Results Of the 35 initially drafted items, 14 were discarded and 19 modified, resulting in a final version with 21 items distributed across three dimensions: warfarin intake (n = 10), self‐care associated with warfarin use (n = 7) and health monitoring (n = 4). The TAAW tool demonstrated a unidimensional structure, excellent internal consistency (Cronbach's alpha = 0.98), high test–retest reliability (Intraclass Correlation Coefficient = 0.96) and strong correlation with the time in therapeutic range (Spearman's rho = 0.91), confirming its validity and reliability. Conclusion The validated TAAW is a robust instrument for assessing adherence to warfarin therapy in clinical and research settings. Its comprehensive approach allows for the identification of adherence patterns, enabling healthcare professionals to implement targeted interventions and optimize anticoagulation outcomes.