Which parameter is essential to monitor for warfarin therapy?

• A. INR.
• B. Renal function.
• C. Hemoglobin.
• D. Blood pressure.

Answer: (A)

Warfarin’s effect is monitored with the INR because it standardizes the anticoagulant effect across individuals. Warfarin dosing varies with diet, drug interactions, and genetics, so simply measuring a single prothrombin time isn’t reliable. The INR translates the prothrombin time into a consistent scale that shows how thick the blood is—whether it’s within the target range needed to prevent clots without causing excessive bleeding. Clinicians adjust the warfarin dose up or down based on the INR to stay in that therapeutic window for the patient’s condition.

Renal function isn’t the direct tool for guiding warfarin dosing, since kidney performance doesn’t measure how strongly the blood is anticoagulated. Hemoglobin can indicate if bleeding has occurred, but it doesn’t reflect current anticoagulant intensity to guide dose changes. Blood pressure isn’t related to the anticoagulant effect and doesn’t guide monitoring of warfarin therapy.