Apheresis (Greek: "to take away") is a medical technology in which the blood of a donor or patient is passed through an apparatus that separates out one particular constituent and returns the remainder to the circulation. It is thus an extracorporeal therapy. Method Depending on the substance that's being removed, different processes are employed in apheresis. If separation by weight is required, centrifugation is the most common method. Other methods involve absorption onto beads coated with… (More on Apheresis)