Can your genes predict blood thinner effectiveness?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Age 20 years or older * Of Old Order Amish descent Exclusion Criteria: * Currently pregnant or less than 6 months have passed since delivery * Currently breast feeding * Has a history of a bleeding disorder or major spontaneous bleed, such as peptic ulcer, epistasis, or intracranial bleed * Has severe hypertension, defined by a blood pressure above 160/95 mm Hg * Takes medications that would affect the outcome(s) to be measured and cannot willingly and safely, in the opinion of the treating physician and study physician, discontinue these medications for 1 week prior to protocol initiation * Is taking vitamins or other supplements and is unwilling to discontinue use for at least 1 week prior to study * Has a coexisting malignancy * Has a creatinine level greater than 2.0 mg/dl, aspartate transaminase (AST) or alanine transaminase (ALT) greater than two times the upper limit of normal, hematocrit less than 32%, or a thyroid-stimulating hormone (TSH) less than 0.4 or greater than 5.5 mIU/L * Has a bleeding disorder or history of gastrointestinal bleeding or other major bleeding episode * Is currently taking aspirin, clopidogrel, or anti-coagulants, such as warfarin, heparin, or GPIIb/IIIa antagonists, and have conditions that might place the participant at increased risk from withdrawal of these medications 14 days prior to protocol initiation * History of unstable angina, heart attack, angioplasty (including stent placement), coronary artery bypass surgery, atrial fibrillation, stroke or transient ischemic attacks, diabetes, or deep vein thrombosis or other thrombosis * Has polycythemia, or thrombocytosis, defined by a platelet count greater than 500,000 * Has thrombocytopenia, defined by a platelet count less than 75,000 * Has had surgery within the last 6 months * Has an aspirin or clopidogrel allergy