Certified Medical-Surgical Registered Nurse Practice Exam

Which laboratory value indicates that warfarin is at therapeutic levels?

1. PTT 1½ to 2 times the control

2. PT 1½ to 2 times the control

3. INR of 3 to 4

4. Hematocrit of 32%

The correct answer is: PT 1½ to 2 times the control

Warfarin is an anticoagulant used to prevent thromboembolic events, and its effectiveness is monitored through specific laboratory values. The prothrombin time (PT) and international normalized ratio (INR) are key indicators of warfarin therapy. When evaluating the therapeutic levels of warfarin, the most relevant value is the INR. In most cases, a target INR of 2 to 3 is indicative of effective anticoagulation for various conditions, such as atrial fibrillation or venous thromboembolism. However, certain clinical scenarios may require a higher INR target, typically up to 4. For the therapeutic monitoring of warfarin, this INR range ensures that the anticoagulation effect is sufficient to prevent clot formation without significantly increasing the risk of bleeding complications. While PTT is primarily associated with monitoring unfractionated heparin therapy, it does not apply to warfarin management. A hematocrit level, while important for assessing overall patient status, does not provide specific information regarding warfarin anticoagulation. Therefore, by assessing the PT and focusing on achieving an appropriate INR level, healthcare providers can ensure that patients are receiving the right dose of warfarin for their medical needs.