The purpose of this research is to study how red blood cells (RBCs) survive in a person's circulation, and how that survival may be different in red blood cells that are donated and stored prior to being transfused. Investigators will study this by collecting blood samples from participants, "labeling" RBCs with a naturally occurring vitamin, biotin. The RBCs will then be re-infused back into the participant and blood samples will be taken weekly for 10 weeks to assess the number of labeled cells in the samples.