What laboratory value will Aspirin and Clopidogrel primarily affect?

Aspirin irreversibly inhibits cyclooxygenase (COX-1), blocking thromboxane A2 synthesis and impairing platelet aggregation for the platelet's lifespan (~7-10 days). Clopidogrel irreversibly blocks the P2Y12 ADP receptor on platelets, also inhibiting aggregation. Both drugs affect platelet function rather than platelet count or the coagulation cascade. PT/INR reflects the extrinsic pathway (affected by warfarin), and PTT reflects the intrinsic pathway (affected by heparin). For most routine dental procedures, patients on aspirin or clopidogrel do not need to stop their medication.