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and anti-B

The percentage of blood types in human populations reflects history and migration patterns. Type B blood is found in 5% to 10% of the English and Irish, but gradually increases eastward, reaching 25% to 30% in the former Soviet Union. Blood type frequencies can also reveal who were conquerors and who were conquered. For example, the frequencies of ABO blood types are very similar in northern Africa, the Near East, and Southern Spain—exactly the places where Arabs ruled until 1492.

The major concern in blood transfusion procedures is that the cells in the donated blood not clump due to antibodies present in the recipient's plasma. That is, the recipient's red blood cells must not contact antibodies against its own ABO antigens. For example, a person with type A (anti-B) blood must not receive blood of type B or AB, either of which would clump in the presence of anti-B in the recipient's type A blood. Likewise, a person with type B (anti-A) blood must not be given type A or AB blood, and a person with type O (anti-A and anti-B) blood must not be given type A, B, or AB blood (fig. 14.22).

Because type AB blood lacks both anti-A and anti-B antibodies, an AB person can receive a transfusion of blood of any other type. For this reason, type AB persons are sometimes called universal recipients. However, type A (anti-B) blood, type B (anti-A) blood, and type O (anti-A and anti-B) blood still contain antibodies (either anti-A and/or anti-B) that could agglutinate type AB cells. Consequently, even for AB individuals, it is always best to use donor blood of the same type as the recipient blood. If the matching type is not available and type A, B, or O is used, it should be transfused slowly and in limited amounts so that the donor blood is well diluted by the recipient's larger blood volume. This precaution usually avoids serious reactions between the donor's antibodies and the recipient's antigens.

Type O blood lacks antigens A and B. Therefore, this type theoretically could be transfused into persons with blood of any other type. Individuals with type O blood are sometimes called universal donors. Type O blood, however, does contain both anti-A and anti-B antibodies, and if it is given to a person with blood type A, B, or AB, it too should be transfused slowly and in limited amounts to minimize the chance of an adverse reaction. When type O blood is given to blood types A, B, or AB, it is generally transfused as "packed cells," meaning the plasma has been removed. This also minimizes adverse reactions due to the anti-A and anti-B antibodies found in the plasma of type O blood. Table 14.14 summarizes preferred blood types for normal transfusions and permissible blood types for emergency transfusions.

H Distinguish between antigens and antibodies. Q What is a blood type?

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