Dietary Vitamin K in Oral Anticoagulation Patients: Clinician Practices and Knowledge in Outpatient Settings

Abstract

Background: Dietary vitamin K is a recognized variable associated with oral anticoagulant therapy. However, current practices of dietary education and instruction regarding vitamin K, as well as factors influencing related decision-making, are unknown. Research has examined healthcare providers' ability to identify a meal containing vitamin K, but the ability to classify portions of specific vegetables according to vitamin K content has not been evaluated. Objective: To characterize dietary evaluation and instructional methods provided to patients receiving warfarin therapy, assess factors influencing instructional methods, and evaluate clinician knowledge of vitamin K content for specific vegetable portions. Methods: A cross-sectional online survey of US healthcare providers involved with management of outpatient oral anticoagulation therapy was conducted. Results: One hundred twenty-two responses were received. Seventy-four percent of respondents collected initial dietary history from all patients and 52% asked all patients for dietary history at follow-up visits. Taking a verbal dietary history from all patients was significantly associated with larger clinic size and managing patients in person. Eighty-two percent of respondents reported providing dietary vitamin K education to all patients. Low patient literacy was a common factor influencing instruction to avoid foods high in vitamin K. Overall mean score reflecting the ability to classify vegetable portions by vitamin K content was 64.6 ± 10.9%. Conclusions: Acquisition of dietary history by anticoagulation providers is not always completed at initial and follow-up patient visits. Provision of patient education at initial visits is relatively high. Patient factors such as low literacy may influence a clinician's decision to provide a specific method of dietary instruction, including avoidance of foods high in vitamin K. Clinicians are least likely to correctly identify vegetable portions containing vitamin K in the range of 10–99 μg and should consider portion size when assessing dietary history.