Which laboratory test is used to monitor anticoagulation therapy for patients on warfarin?

The International Normalized Ratio (INR) is the correct laboratory test used to monitor anticoagulation therapy in patients taking warfarin. Warfarin is an anticoagulant that works by inhibiting the vitamin K-dependent clotting factors, which requires careful monitoring to ensure therapeutic effectiveness while minimizing the risk of bleeding.

The INR provides a standardized measure of how well and how quickly the blood clots; it's derived from the Prothrombin Time (PT). Monitoring INR is essential because it allows healthcare providers to adjust the warfarin dosage accordingly to maintain the INR within the target therapeutic range, typically between 2.0 and 3.0 for most indications, but it can vary based on the condition being treated.

While the Prothrombin Time may indicate how well anticoagulation is working, it is the INR that provides a more consistent and reliable measure, regardless of the laboratory performing the test. Other tests such as the Complete Blood Count (CBC) assess different aspects of blood health and cannot evaluate coagulation specifically for warfarin therapy. Similarly, the Activated Partial Thromboplastin Time (aPTT) is used for monitoring other anticoagulants, mainly those that affect the intrinsic pathway of coagulation, such as