Until the late 1970s, most blood was transfused without being further processed to separate plasma or platelets. This was termed ‘whole blood’. Current practice in many EU countries is to process most or all whole blood donations into components – red cells, platelets and plasma.
In a typical blood establishment process, 450-500 ml of the donor’s blood is drawn into a plastic pack containing 63 ml of an anticoagulant-preservative solution such as Citrate Phosphate Dextrose (CPD) or CPD–Adenine. The citrate binds calcium and acts as an anticoagulant, and the glucose and adenine support red cell metabolism during storage. The whole blood unit may be filtered to remove white cells, most of the plasma is removed, and an additive solution, formulated to support erythrocyte metabolism, is added to the remaining red cells.
Platelet concentrate may be prepared either from the white cell and platelet layer (the so-called buffy coat) or from platelet rich plasma. Red cells, platelets, plasma and white cells can also be collected by apheresis.
Directive 2002/98 EC lists names and specifications of red cell, platelet and plasma components. These are summarised in table 6.1 at the end of this chapter. This section of the manual provides information about some of these components that are in common use.
In the manual, the term ‘red cell unit’ is used to denote the red cells from one standard blood donation.