Aphaeresis is the process of removing a Specific component of the blood, such as platelets, and returning the remaining components, such as red blood cells and plasma, to the donor. This process allows more of one particular part of the blood to be collected than could be separated from a unit of whole blood. Aphaeresis is also performed to collect plasma (the liquid part of the blood) and granulocytes (white blood cells). The Therapeutic Aphaeresis Unit uses special machines to remove disease-causing substances and cells from the blood of patients. In addition, the unit also collects stem cells for blood and bone marrow transplantation.