Aspirin resistance among long-term aspirin users after carotid endarterectomy and controls: Flow cytometric measurement of aspirin-induced platelet inhibition

Activation of platelets by arachidonic acid (ARA): all 86 patients receiving long-term low-dose aspirin medication (ASP) showed inhibition of ARA-induced platelet activation (ie, <15% CD62p-positive platelets), whereas two of 29 patient controls without reported history of aspirin intake (PCON) demonstrated cyclooxygenase inhibition. The threshold of 15% is marked by the dashed line.

PFA-100 collagen-epinephrine closure time (CEPI-CT): 14 of 86 patients showed a normal CEPI-CT despite long-term low-dose aspirin medication (ASP). Four of 29 patient controls without an apparent history of aspirin intake (PCON) had an elevated CEPI-CT. The upper reference limit (165 seconds) is marked by the dashed line.