American Board of Family Medicine (ABFM) Practice Exam 2026 - Free ABFM Practice Questions and Study Guide

To understand why hypothyroidism would require a higher dose of warfarin to maintain an appropriate INR in a patient with atrial fibrillation, it’s important to consider the role of thyroid hormones in various physiological processes. Thyroid hormones have a significant influence on metabolism, and their deficiency can lead to decreased metabolic function which affects the elimination of warfarin in the body. When thyroid function is impaired, the clearance of warfarin may be reduced, requiring the clinician to increase the dose to achieve the desired anticoagulation effect.

Maintaining an effective INR in patients on warfarin therapy is crucial, especially to prevent thromboembolic complications associated with atrial fibrillation. In patients with hypothyroidism, the body's reduced metabolic rate can prolong the half-life and enhance the anticoagulant effects of warfarin, leading to a potential need for adjusting the warfarin dose upward if the INR is not adequately maintained.

In contrast, factors like malnutrition, heart failure, and acute kidney injury typically lead to either a decreased requirement for warfarin or present complexities that could complicate therapy. Malnutrition may affect protein levels (like albumin), which is important for warfarin binding, potentially requiring less warfarin. Similarly