Blood Supply

Blood units are collected in the United States by the American Red Cross and by blood banks at local hospitals. Donations are always needed due to the constant demands of hospitals and their trauma units as well as to the brief shelf-life of stored blood. Some 12 million units are used every year in the U.S.

Blood is collected by simply inserting a needle into a vein and allowing the blood to flow into a plastic bag that has been specially treated to prevent the blood from clotting. The average adult human has approximately 6 qt (5.7 l) of blood in their body, so the loss of 1 pt (0.5 l) will have little effect on them. The liquid portion of the blood is quickly replaced from fluid the donor drinks afterwards and the blood cells are regenerated from the bone marrow. Healthy donors can make blood donations about every six to eight weeks without suffering any ill effects.

Once the blood has been collected in the bag, other small specimens are collected for testing. Blood is tested for hepatitis viruses, syphilis, AIDS, or other diseases and classified as to type. Technicians also run a series of antigen tests to provide information on the presence of any factor that may provoke a reaction in the recipient.

After the blood is tested and found satisfactory it is refrigerated for use. Blood in blood banks is distributed to medical facilities in the region of the blood bank. Patients undergoing surgery have blood tests to determine their blood type and antigen structure so that compatible blood can be selected to replace that which is lost during surgery. Patients who arrive in the emergency room following a trauma such as an automobile accident also are tested for possible blood replacement. Loss of between 1-2 qt (1-2 l) of blood will result in shock and require the immediate transfusion of blood. Loss of up to 3 qt (2.8 l), half the blood supply in the human body, can be fatal.