Benchmark II Medical-Surgical Nursing Practice Test

Warfarin monitoring relies on a standardized measure that reflects the extrinsic coagulation pathway. Warfarin inhibits vitamin K–dependent clotting factors, which lengthens the prothrombin time. Because PT results vary with reagents and labs, they are converted into the International Normalized Ratio, a standardized value that allows consistent assessment of anticoagulation across settings. Clinicians use the INR to adjust warfarin dosage and keep patients within a target therapeutic range, typically around 2.0–3.0 for many indications (with higher ranges for some mechanical valves). The other tests serve different purposes: aPTT is used for monitoring unfractionated heparin, and platelet count measures platelets rather than the effect of warfarin. PT alone isn’t reliable across labs, which is why INR is preferred.