A patient taking warfarin needs a minor oral surgical procedure. Which laboratory test best assesses their anticoagulation status?

Warfarin inhibits vitamin K-dependent factors (II, VII, IX, X) affecting the extrinsic/common pathway, monitored by prothrombin time standardized as the INR. Most simple dental procedures can proceed with an INR of about 3.0 to 3.5 or lower without stopping warfarin.Other options: aPTT monitors the intrinsic pathway (heparin); bleeding time and platelet count assess platelet function/number, not warfarin effect.Key exam takeaway: Warfarin = check PT/INR; heparin = aPTT. Do not routinely stop warfarin for simple dental surgery if the INR is therapeutic.