This is a platelet transfusion study. The purpose of this study is to measure the life span and quality of platelets stored in a refrigerator. Participants will give platelets by apheresis. Platelets will be stored for 3 -20 days. A small portion of the subject's own stored platelets will be tagged with a radioactive isotope and infused back into the participant. This will enable us to track how many transfused platelets survive after storage in the refrigerator.