When blood is spun in a centrifuge, it separates into two main components:

• plasma—the yellow liquid component on top, and
• red cells—the dark cellular part on the bottom

Similarly, when someone donates a unit of blood, it can be "spun down" in a centrifuge and separated into separate components. The separated components are shown below. Patients usually only need one type of component (for example, red cells if they have been in an accident, platelets if they are on chemotherapy and their bone marrow has shut down, or plasma, if they are having coagulation problems), and separation allows a single donation to benefit up to four different patients.

This is a unit of "packed red cells," what most people generally think of as a "unit of blood." It has the plasma component removed, and also possibly the platelets. This is a unit of O-negative red cells (the O in the upper right hand corner of the label is the blood type—or blood "group" to be technically correct—and the fact that it is outlined and not solid indicates the unit is Rh-negative. This is the type of red cells that can go to anyone, without causing bad reaction.

Red cells are stored at 1-6 C, for about 6-weeks (depending on which preservative solution they are stored in).

This is a unit of Fresh Frozen Plasma. It must be stored frozen to preserve the coagulation factors, which would deteriorate too quickly if it were kept in a refrigerator. This unit is from a group B-positive donor.

Fresh Frozen Plasma must be stored at -18 C and is good for up to one year.

This is a unit of Platelets, more specifically, Platelets, Pheresis. It was obtained from one donor in a special procedure called "pheresis." This donor did not donate red cells, just platelets. This is one "dose" of platelets. If a patient needs a platelet transfusion, he must get about six units of platelets taken from a whole blood donation to match the dosage from this single unit. We do not used platelets from whole blood donations in our hospital, and most hospitals on the West Coast don't, either. This unit is from an O-positive donor.

Platelets must be stored at room temperature, in an "agitator" that keeps them moving (this helps keep them well-oxygenated). Platelets must be used within 5 days of donation, or else they are wasted.

This is a unit of Cryoprecipitated Anti Hemophilic Factor (cryoprecipitate, cryo) from an AB-positive donor. Cryo is separated from Fresh Frozen Plasma (long story, not here...).

Cryo is used as a source of fibrinogen, Factor XIII, and fibronectin. It is also a second-line source to treat Factor VIII deficiency (hemophilia A) and von Willebrand's Disease.