Healthy subjects that reported no use of aspirin or NSAID in the 10 days prior to participation, no bleeding disorders, nor any other significant medical history, were selected for participation in this study. Blood was drawn using a 21-gauge needle. The first 2ml was discarded and the remaining blood was collected into a vacutainer tube containing EDTA for complete blood count (CBC) and vacutainers containing 3.2% (0.105 moles/liter) sodium citrate for LTA (Becton Dickenson, Franklin Lakes, NJ). Complete blood count was performed within 30 minutes of phlebotomy. Blood drawn into citrated vacutainers were randomly selected to be spun at 150 × g, 200 × g, 300 × g, and 500 × g for 10 minutes, each separated by 30 minutes intervals. The order of centrifugation was random in each of the 10 samples. In earlier samples, tubes were also spun at 80 ×g and 120 × g, but samples did not yield sufficient PRP to perform an adequate number of LTA runs.