In monitoring warfarin therapy, which test is used to assess anticoagulation status?

• A. INR monitoring
• B. Hematocrit
• C. Platelet count
• D. Prothrombin time

Answer: (A)

INR monitoring is used for warfarin therapy because warfarin lowers the production of vitamin K–dependent clotting factors, which lengthens the time it takes blood to clot. PT measures this clotting time, but results vary depending on the lab’s reagents. The INR converts PT to a standardized value, accounting for those differences, so clinicians can reliably compare results across labs and adjust warfarin dosing to stay within the therapeutic range. Hematocrit and platelet count don’t reflect anticoagulation status, and while PT relates to coagulation, the INR is the standardized, clinically used measure for monitoring warfarin. Typical therapeutic INR ranges are about 2.0–3.0 for many conditions (2.5–3.5 for some mechanical valves).