Autologous blood transfusion is a major problem in a wide range of competitive sports. Methods with increased sensitivity, specificity, and feasibility are needed to identify athletes who cheat in this manner and compromise their health and the integrity of their sports in general. Complete blood counts (CBC) offer routine high-resolution assessment of the current hematologic status of individuals, providing estimates of a number of blood characteristics, such as the total hemoglobin concentration in the blood (HGB) and the volume fraction of cells in the blood (HCT). These CBC components are homeostatically controlled by the carefully regulated dynamic processes of red blood cell (RBC) production in and release from the bone marrow, RBC maturation in the peripheral circulation over the course of the ~100-day RBC lifespan, and clearance and recycling of senescent cells. Any significant perturbation to the circulating population of RBCs, like autologous transfusion, will immediately trigger compensatory modulation of one or more of these dynamic processes. The investigators believe quantification of these underlying dynamic processes will enable us to detect autologous transfusion. These dynamic RBC processes cannot currently be measured directly, but novel mathematical modeling enables their inference from routine complete blood and reticulocyte counts. The investigators propose to test the ability of modeled RBC dynamics to identify instances of autologous blood transfusion.