Which laboratory value is used to monitor warfarin therapy?

Which laboratory value is used to monitor warfarin therapy?

• A. aPTT
• B. Platelet count
• C. INR
• D. Hematocrit

Answer: (C)

Monitoring warfarin therapy hinges on assessing its effect on vitamin K–dependent clotting factors using the international normalized ratio. Warfarin blocks the synthesis of factors II, VII, IX, and X, so the prothrombin time (PT) becomes prolonged. The INR standardizes PT results across different labs, making it the preferred metric to adjust warfarin dosage and keep patients in the therapeutic range. In contrast, the aPTT measures the intrinsic pathway and is used to monitor unfractionated heparin, not warfarin. Platelet count reflects platelets and helps assess bleeding risk related to platelet disorders or drug effects that involve platelets, but it does not indicate warfarin’s level of anticoagulation. Hematocrit indicates red blood cell volume and is used to evaluate anemia or blood loss, not anticoagulation status.

Monitoring warfarin therapy hinges on assessing its effect on vitamin K–dependent clotting factors using the international normalized ratio. Warfarin blocks the synthesis of factors II, VII, IX, and X, so the prothrombin time (PT) becomes prolonged. The INR standardizes PT results across different labs, making it the preferred metric to adjust warfarin dosage and keep patients in the therapeutic range.

In contrast, the aPTT measures the intrinsic pathway and is used to monitor unfractionated heparin, not warfarin. Platelet count reflects platelets and helps assess bleeding risk related to platelet disorders or drug effects that involve platelets, but it does not indicate warfarin’s level of anticoagulation. Hematocrit indicates red blood cell volume and is used to evaluate anemia or blood loss, not anticoagulation status.