Pheresis is a medical term for a procedure in which blood is removed from the body, separated into components like platelets, white blood cells, and red blood cells, and then part of it is returned to the patient. There are several synonyms that are used for pheresis such as plasma exchange, therapeutic apheresis, blood fractionation, and hemapheresis. Plasma exchange refers to the separation of blood plasma from blood cells; therapeutic apheresis is a treatment that removes disease-causing substances from the blood; blood fractionation implies separating blood constituents into fractions while preserving their biologic activity; and hemapheresis is a process of removing a specific component of blood from the body for therapeutic purposes. These terms are often used interchangeably to describe the same procedure.