Which test measures platelet function?

• A. Complete blood count
• B. PT/INR
• C. Bleeding time
• D. Anti-phospholipid antibodies

Answer: (C)

Bleeding time directly assesses how well platelets function in forming a primary hemostatic plug. After a standardized skin incision, the time until the bleeding stops depends on platelet adhesion, activation, and aggregation to seal the vessel. A prolonged bleeding time suggests impaired platelet function, as seen with aspirin effect or von Willebrand disease. The other options relate to different parts of hemostasis: a complete blood count checks how many platelets are present, PT/INR evaluates the extrinsic coagulation pathway and clotting factors, and anti-phospholipid antibodies identify autoimmune antibodies associated with clotting disorders rather than direct platelet function.