The page below is a sample from the LabCE course Antiplatelet Medication Response Testing: Aspirin and Clopidogrel. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Aspirin Resistance

Several studies conducted within the past five years concluded that 5-40% of individuals who take aspirin every day to help prevent heart attacks and strokes may not benefit from the anticoagulant effect of aspirin.* A person is considered aspirin-resistant if:
  • The individual is using aspirin therapeutically (75-150 mg/day) and an ischemic cardiac event occurs
  • Laboratory testing determines a lack of antiplatelet effect, despite therapeutic dosing for at least five days
An algorithm, such as the one shown on the following page, may be a useful tool for determining whether platelet function testing should be ordered.

* It should be noted that a study published in 2012 concluded that aspirin resistance is very rare. However, the sample group of 400 individuals in this study were all relatively young and healthy. In previous studies, sample groups included individuals who were at high risk for cardiac events, for example, a cohort of patients with metabolic syndrome. An abstract of the article for the 2012 study is available at: Accessed February 18, 2016.