In monitoring a patient on oral anticoagulant therapy, an INR of 1.3 was obtained. How would you interpret this result?

• A. The patient is adequately anticoagulated and should be tested again in 1 month.
• B. The patient is underanticoagulated and should be evaluated for a change in dietary habits.
• C. The patient is overanticoagulated and should receive a vitamin K injection.
• D. Data to determine the patient's status are insufficient.

Answer: (B)

INR values guide how effectively a patient on warfarin is anticoagulated. For most conditions, the therapeutic target is about 2.0–3.0; an INR of 1.3 is below that range, meaning the patient is underanticoagulated and at risk for thrombosis. The next steps focus on bringing the INR into the target range and maintaining stability. Tooling this up typically involves adjusting the warfarin dose and reviewing factors that can alter INR. Diet is one such factor: intake of vitamin K–rich foods (like leafy greens) can lower the INR, while very low or inconsistent intake can cause fluctuations upward or downward. Therefore, when an INR is subtherapeutic, it’s important to evaluate dietary vitamin K intake and adherence, identify any interactions or changes that could be reducing warfarin effect, and then adjust the dose to achieve and maintain the desired range.