Allogeneic (donor) blood transfusions are often required during and/or after orthopedic hip surgery to maintain adequate hemoglobin concentration, prevent tissue ischemia, treat hypotension, and compensate for fluid shifts. For example, during hospitalization for hip replacement, patients may receive up to two to three units of blood. This amount varies depending on the technical difficulty of the surgery, the patient's hemoglobin concentration prior to surgery, and the patient's clinical status.