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BACKGROUND: Cytochrome P450 2C19 genotype has been shown to modify cardiovascular outcomes on clopidogrel therapy in patients post-acute coronary syndromes or percutaneous coronary interventions. Recent clopidogrel label changes have incorporated this information; however real-world application of genetic testing in patients receiving thienopyridine antiplatelet therapy is unknown. METHODS: A retrospective, integrated medical and pharmacy claims database, cohort analysis was conducted in patients with new clopidogrel or prasugrel prescriptions between 7/1/08-6/30/10, and continuous eligibility for 6 months pre- and 3 months post-initiation. Genetic testing was identified using CPT-4 codes present 1 month prior and 3 months post the index prescription date. Genetic testing incidence was calculated, and univariate comparisons of prescriber information, and patient demographic and clinical characteristics in cases tested vs not tested were performed. RESULTS: The analysis included 95,381 clopidogrel and 1,819 prasugrel patients. Genetic testing was recorded in 522 (0.6%) clopidogrel and 15 (0.8%) prasugrel patients, rendering the latter sample too small for detailed analysis. Clopidogrel patients receiving genetic testing (vs patients not tested) were a mean age of 58±13 yrs (68±13 yrs, p CONCLUSION: Although the FDA has provided numerous advisories that have lead to changes in clopidogrel provider information sheets, genetic testing is rarely employed in routine practice in patients prescribed clopidogrel or prasugrel therapy. Testing was biased toward younger clopidogrel patients with a recent stroke event, and non-cardiologist prescribers. While these data establish a national benchmark for future comparison, further exploration of barriers to testing, provider education and patient selection, and the impact of programmatic approaches to testing are warranted.