Which lab value is used to monitor warfarin therapy?

Which lab value is used to monitor warfarin therapy?

• A. INR
• B. aPTT
• C. ALT
• D. Creatinine

Answer: (A)

The main idea here is how warfarin’s effect is tracked in the blood. Warfarin reduces the already-made vitamin K–dependent clotting factors, which slows the clotting process via the extrinsic pathway. The test that best reflects this in a standardized way across different laboratories is the international normalized ratio (INR), derived from the prothrombin time. Using INR allows clinicians to adjust warfarin dosing to keep the level within a therapeutic range (often about 2.0–3.0 for many conditions, sometimes higher for certain mechanical heart valves). The other tests aren’t used to monitor warfarin: aPTT is for heparin monitoring, while ALT and creatinine assess liver and kidney function, respectively, not anticoagulation status.

The main idea here is how warfarin’s effect is tracked in the blood. Warfarin reduces the already-made vitamin K–dependent clotting factors, which slows the clotting process via the extrinsic pathway. The test that best reflects this in a standardized way across different laboratories is the international normalized ratio (INR), derived from the prothrombin time. Using INR allows clinicians to adjust warfarin dosing to keep the level within a therapeutic range (often about 2.0–3.0 for many conditions, sometimes higher for certain mechanical heart valves). The other tests aren’t used to monitor warfarin: aPTT is for heparin monitoring, while ALT and creatinine assess liver and kidney function, respectively, not anticoagulation status.