People have been donating blood sincethe early twentieth century to help acci-dent victims and patients undergoingsurgical procedures. Usually a pint ofwhole blood is donated, and it is thendivided into platelets, white blood cells,and red blood cells. People can donateblood (for red blood cells) about onceevery two months.Transfusing the blood from the donorto the recipient is straightforward. Itinvolves taking the blood from a donor’sarm vein by means of a hypodermicsyringe. The blood flows through a plas-tic tube to a collection bag or bottle thatcontains sodium citrate, which preventsthe blood from clotting.When the blood is given to a patient, aplastic tube and hypodermic needle areconnected to the recipient’s arm. Theblood flows down from the container bygravity. This is a slow process and maylast as long as 2 hours to complete theinfusion of blood into the recipient. Thepatient is protected from being infectedduring the transfusion. Only sterile con-tainers, tubing, and needles are used,and this helps ensure that transfused orstored blood is not exposed to disease-causing bacteria.Negative reactions to transfusions arenot unusual. The recipient may sufferan allergic reaction or be sensitive todonor leukocytes. Some may suffer froman undetected red-cell incompatibility.Unexplained reactions are also fairlycommon. Although they are rare, othercauses of such negative reactions in-clude contaminated blood, air bubbles inthe blood, overloading of the circulatorysystem through administration of ex-cess blood, or sensitivity to donor plasmaor platelets
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