Blood doping is the practice of boosting the number of red blood cells (RBCs) in the circulation in order to enhance athletic performance. Because they carry oxygen from the lungs to the 1) ___, more RBCs in the blood can improve an athlete’s aerobic capacity (VO2 max) and endurance. In 1993, U.S. Special Forces commanders at Fort Bragg started experimenting with blood doping. Special forces operators would provide two units of whole blood, from which red blood cells would be extracted and concentrated. Twenty-four hours before a mission, a small amount of RBCs would be infused back into the soldier. It was believed that the procedure would increase the soldiers’ endurance and alertness. The term blood doping originally meant doping with blood, i.e. the transfusion of RBCs. There are two possible types of transfusion: homologous and 2) ___. In a homologous transfusion, RBCs from a compatible donor are harvested, concentrated and then transfused. In an autologous transfusion, the athlete’s own RBCs are harvested well in advance of competition and then re-introduced before a critical event. Both types of transfusion can be dangerous because of the risk of 3) ___ and the potential toxicity of improperly stored blood. In athletic competitions, from a logistical standpoint, either type of transfusion requires the athlete to surreptitiously transport frozen RBCs, thaw and re-infuse them, and then dispose of the medical paraphernalia. In the late 1980s, an entirely new form of blood doping involved the hormone erythropoietin (EPO). EPO is a naturally-occurring growth factor that stimulates the creation of RBCs. Recombinant EPO is a pharmaceutical product for the treatment of anemia resulting from renal failure or 4) ___ chemotherapy. Pharmaceutical EPO can boost hematocrit for six weeks or longer. Excessive use of the EPO can cause polycythemia, a condition where the level of RBCs in the blood is abnormally high. This causes the blood to be more 5) ___ than normal, a condition that strains the heart. Some elite athletes who died of heart failure – usually during sleep, when heart rate is naturally low – were found to have unnaturally high RBCs. The simple act of increasing the number of RBCs in the blood stream makes blood thicker which can also make it clot more readily. This can increase in the chances of heart attack, stroke, and pulmonary 6) ___. Blood contamination during preparation or storage can lead to sepsis. A test for detecting homologous blood transfusions has been in use since 2000. The test is based on a technique known as fluorescent-activated cell sorting. By examining markers on the surface of blood cells, it can be determined whether blood from more than one person is present in an athlete’s blood. In 2000 a test was developed to detect pharmaceutical EPO by distinguishing it from the nearly-identical natural hormone normally present in an athlete’s 7) ___. The test method relies on scientific techniques known as gel electrophoresis and isoelectric focusing. Although the test has been widely applied, especially among cyclists and triathletes, it is controversial. The principal criticism has been toward the ability of the test to distinguish pharmaceutical EPO from other proteins that may normally be present in the urine of an athlete after strenuous exercise.

ANSWERS:
1) muscles; 2) autologous; 3) infection; 4) cancer; 5) viscous; 6) embolism; 7) urine

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