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The donated blood is sealed in a special plastic bag that contains substances that will keep it from clotting (anticoagulants) and will preserve it. Refrigerated, whole blood is useable for 42 days. Blood components, however, can be preserved for much longer--in the case of red blood cells, up to 10 years, if frozen. A sample of the donated blood is taken for testing. It is checked for infections diseases like AIDS and syphilis, for anaemia, and, if the blood type is not already known, for blood typing. Human blood falls into three major groups, A, B, and O; the types get their names from certain molecules found on the surface of the red blood cells. If a person receives a donation of an incompatible blood type, the blood cells can clump together, a dangerous and possibly fatal situation. Type O blood can be received by persons with A, B, or AB blood (which is why type O is sometimes called the "universal donor"), but a person with Type O blood can only Type O blood. It is also important to match the Rh factor of the blood, which can be positive or negative.
Anyone in good health can donate blood. It is generally recommended that the donor be over age 17 (although some states allow younger persons to donate, with their parent's permission) and weigh at least 110 pounds. The donor's body will replenish the donated blood quickly. However, it's best to not give blood than once every two months. There are several special donation procedures. Persons who are expecting to undergo surgery may opt to donate several pints of their own blood, which is stored and given back to them during the surgery. This is called an autologustranfusion.
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