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LEARNING OBJECTIVES
After studying this chapter you should be able to:
Describe the structures of the ABO and Rh blood group antigens.
Understand how blood is typed and cross-matched.
Name the clinical and laboratory features of acute and delayed transfusion reactions.
Identify and prioritize the different risks associated with blood transfusion.
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In 1492, as Pope Innocent VIII lapsed into a coma, the blood of three boys was infused—into his mouth! Considerable progress has been made since then, particularly following Karl Landsteiner's discovery of the ABO blood group antigens in 1901. Blood transfusions have had a larger impact on medicine and surgery than any other therapeutic advance in hematology. In the United States, approximately 15 million units of blood are transfused each year.
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This chapter begins with the fractionation of donor blood into cellular and plasma components that are used in transfusion. An overview of the important blood group antigens is followed by a consideration of methods used for typing and cross-matching units of blood. After reviewing the indications for transfusing red cells, platelets, and plasma, we discuss the hemolytic, immunologic, inflammatory, and infectious risks posed by transfusion therapy. The chapter ends with a perspective on current and future developments in transfusion medicine.
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DONOR BLOOD COMPONENTS
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The standard blood donation involves phlebotomy through a large-bore needle inserted into an arm vein. Approximately 450 mL are transferred into a sterile plastic bag containing citrate phosphate dextrose (CPD)-adenine. Citrate (C) prevents coagulation by chelating calcium ions. The phosphate (P) buffer maintains the pH at physiologic levels. Dextrose (D) provides a source of energy during blood storage. Adenine enhances the viability of the stored red cells.
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As noted in Chapter 1, when a tube of anticoagulated blood sediments in a gravitational field, the relatively dense red cells go to the bottom, and the less dense white cells and platelets form a "buffy coat" layer on the upper surface of the red cells, whereas cell-free plasma is least dense and collects at the top of the tube. In the blood bank, the bag of freshly collected donor blood is first centrifuged at relatively low speed, allowing separation into packed red cells and platelet-rich plasma (Fig. 25-1). The platelet-rich plasma is then spun at a higher speed, enabling separation into cell-free plasma and a platelet concentrate (Fig. 25-1).
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Packed red cells are stored at 4°C for up to 42 days. In most medical centers, the white blood cells are removed by a filter, a maneuver that lowers the incidence of febrile reactions and human leukocyte antigen (HLA) alloimmunization and reduces the risk ...