1. The process of removing a specific component from blood and returning the remaining components to the donor, in order to collect more of one particular part of the blood than could be separated from a unit of whole blood: "Apheresis (af uh REE sis) takes longer than a whole blood donation which usually takes about 10-20 minutes to collect the blood, while an apheresis donation may take about one to two hours."
2. In linguistics, apheresis (uh FER i sis) is the omission at the beginning of a word as in "coon" for "raccoon"; "till" for "until"; "squire" for "esquire"; "count" for "account"; or "special" for "especial".

Removal of unwanted or pathological components from a patient's blood by means of a continuous-flow separator: "The therapeutic apheresis is similar to the process of hemodialysis, because detoxified blood is returned to the patient."

"The removal of cellular material is termed cytapheresis; leukapheresis describes the removal of leukocytes only. Plasmapheresis, also called plasma exchange, involves removal of noncellular materials."

Therapeutic aspharesis has been used to treat blood hyperviscosity, cold agglutinin hemolytic anemia, posttransfusion purpura, thkrombotic thrombocytopenic purpura, myasthenia gravis, sickle cell anemia, Guillain-Barre syndrome, familial hypercholesterolemia, and even certain drug overdoses."