Which drug is known to prolong bleeding time without altering platelet count?

• A. Aspirin
• B. Warfarin
• C. Heparin
• D. Vitamin K

Answer: (A)

Bleeding time reflects platelet function, not the number of platelets or the coagulation factors. A drug that prolongs bleeding time does so by making platelets less able to stick together, while keeping their count normal. Aspirin does this by irreversibly inhibiting cyclooxygenase-1 in platelets, which blocks thromboxane A2 production and prevents aggregation. So platelets are present but dysfunctional, leading to longer bleeding time without a change in platelet count. In contrast, warfarin and heparin affect the coagulation cascade and prolong tests like PT/INR or aPTT, not bleeding time. Vitamin K influences clotting factor production and would not typically prolong bleeding time.