Disclosed are unique methods for identifying the lowest, yet optimal, aspirin doses for patients. These methods are also characterized as having little to no aspirin-related side-effects. These methods may be used pre- as well as post-thrombotic event, and employs a patient's urinary thromboxane B₂ metabolic levels (e.g., 11-dehydrothromboxane B₂), to identify the patient's platelet activation level. A patient's urinary thromboxane B₂ metabolic level is then used to calculate and appropriate and individualized treatment effective for utilizing platelet activation. Kits for utilizing this technique are also provided. In yet another particular aspect, the invention provides a method for utilizing a random urine sample obtained from a patient to determine whether a patient or particular individual's current dosage of aspirin is providing an adequate and appropriate level of inhibition of platelet activation levels, as compared to inhibition levels observed in individuals not taking aspirin.