It's important that all blood types get donated but it's especially important for O- people to donate as this blood type can be given to anyone. The table below shows the four types of blood and the Rh factor — Rh factor refers to the presence (+) or absence (-) of a certain protein in your blood — how many people have a certain blood type and who can receive a transfusion of each blood type.

Humans average 10 to 12 pints of blood. When you do a whole blood donation, only one pint is removed. The blood is then centrifuged to break it into four components:

• red blood cells (hemoglobin)
• platelets
• plasma
• cryoprecipitate

Red blood cells are used to treat people with anemia and for transfusions during surgery, accidents and childbirth. Platelets, the part of the blood that assists in clotting, is given to cancer patients whose own bone marrow is unable to produce enough. Plasma, the liquid portion of blood, is used to treat shock, burn and accident patients. The last component, cryoprecipitate, is a clotting factor used to treat those with hemophilia — a blood disorder where the blood fails to clot normally due to a lack of one or more clotting factors. It is almost exclusively found in males as it is a recessive trait associated with the X-chromosome.

The blood supply today is extremely safe. You cannot get HIV from donating blood and the risk of transmission of HIV or hepatitis to a transfusion patient has been greatly reduced in recent years due to the tests that are run on every blood donation. Each unit is tested for infectious disease including hepatitis B and C, HIV 1 and 2 and syphilis. If any of these show up during testing, the blood is immediately discarded.