Radioactivity measurements Samples will be obtained from the radiolabeled fresh and stored platelets before infusion and used as a radioactive standard. By measuring the volume infused, the total dose of radioactivity infused will be calculated. In vitro elution of the label from the transfused platelets will be determined by two elution assessment methods, as well as the in vivo elution of radioactivity from the serial blood samples obtained post-infusion of the labeled platelets.