Elevated urinary levels of 11-dehydrothromboxane B2 identify patients who are:
a. At risk for heparin-induced thrombocytopenia
b. Overanticoagulated with warfarin
c. Resistant to aspirin antiplatelet therapy
d. Resistant to direct thrombin inhibitors
ANS: C
11-Dehydrothromboxane B2 is a metabolite derived from thromboxane A2, synthesized by the platelet in the eicosanoid pathway. This pathway is blocked by aspirin's effect on cyclooxygenase. When it is not blocked, and platelet activation occurs, 11-dehydrothromboxane B2 is secreted and found in urine at an elevated level. Thus its elevation indicates that platelet activation is occurring and has not been blocked by aspirin. This is called aspirin resistance.
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