A nurse is reviewing laboratory results for a client who is taking warfarin. Which of the following laboratory tests determines if the dose of medication is within the recommended target range?

Rationale: A. Bleeding time: This test evaluates platelet function and capillary integrity, not anticoagulation status. It is not used to monitor warfarin therapy. B. aPTT: Activated partial thromboplastin time is used to monitor heparin therapy, not warfarin. Warfarin affects different clotting factors primarily measured by PT/INR. C. Factor VIII: This assesses clotting factor levels, particularly relevant in hemophilia A. It does not provide information about warfarin’s anticoagulant effects. D. INR: The International Normalized Ratio is the standard test used to monitor warfarin therapy. It adjusts for variability in PT results and determines if warfarin is in the therapeutic range.