A patient takes both aspirin and clopidogrel. Which laboratory parameter is affected?

Correct answer: C. Platelet function

• A. PROTHROMBIN TIME assesses the extrinsic pathway and is the test for WARFARIN, not for antiplatelet agents.
• B. Platelet COUNT is unchanged. A normal count in a dually antiplatelet-treated patient tells you nothing about their bleeding risk, which is a common source of false reassurance.
• C. CORRECT. Both drugs impair platelet FUNCTION while leaving platelet NUMBER untouched. Aspirin irreversibly acetylates COX-1, abolishing thromboxane A2 synthesis; clopidogrel irreversibly blocks the P2Y12 ADP receptor. Both effects last the LIFETIME of the platelet, roughly 7 to 10 days, because the anucleate platelet cannot synthesise new protein. Neither is captured by a routine coagulation panel — assessment requires platelet function testing or bleeding time, and in practice is made clinically.
• D. PARTIAL THROMBOPLASTIN TIME assesses the intrinsic pathway and is the test for unfractionated HEPARIN.

Note: Do NOT interrupt dual antiplatelet therapy for routine dental surgery — the thrombotic risk of stopping, particularly after recent coronary stenting, exceeds the bleeding risk of continuing. Manage with local measures: atraumatic technique, sutures, oxidised cellulose or gelatin sponge, and tranexamic acid mouthwash.