A patient has been taking aspirin regularly for arthritic pain. Which one of the following tests is most likely to be abnormal in this patient?

A patient has been taking aspirin regularly for arthritic pain. Which one of the following tests is most likely to be abnormal in this patient?

• A. Platelet count
• B. PFA-100
• C. Prothrombin time
• D. Activated partial thromboplastin time

Answer: (B)

Aspirin interferes with platelet function by blocking thromboxane A2 formation, which impairs platelet aggregation. Tests that assess how well platelets form a plug under flow will be affected, making the PFA-100 the most likely abnormal result. Platelet count stays normal because aspirin doesn’t change the number of platelets. Prothrombin time and activated partial thromboplastin time measure the clotting cascade in plasma, not platelet function, so they’re typically normal with aspirin use.

Aspirin interferes with platelet function by blocking thromboxane A2 formation, which impairs platelet aggregation. Tests that assess how well platelets form a plug under flow will be affected, making the PFA-100 the most likely abnormal result. Platelet count stays normal because aspirin doesn’t change the number of platelets. Prothrombin time and activated partial thromboplastin time measure the clotting cascade in plasma, not platelet function, so they’re typically normal with aspirin use.