blood transfusion, transfer of blood from one person to another, or from one animal to another of the same species. Transfusions are performed to replace a substantial loss of blood and as supportive treatment in certain diseases and blood disorders. When whole blood is not needed, or when it is not available, plasma, the fluid of the blood without the blood cells, can be given. Alternately, such components of the blood as red cells, white cells, or platelets may be given for particular deficiencies. Blood substitutes blood substitute, substance that mimics the function of blood. Blood substitutes typically concentrate only on reproducing the function of hemoglobin , the molecule that carries oxygen through the body, and do not attempt to replicate the blood's other functions.
..... Click the link for more information. , which are under development, are expected ultimately to ease the chronic short supply of blood and to alleviate certain storage and compatibility problems.

In whole-blood transfusions, the blood of the donor must be compatible with that of the recipient. Blood is incompatible when certain factors in red blood cells and plasma differ in donor and recipient; when that occurs, agglutinins (i.e., antibodies) in the recipient's blood will clump with the red blood cells of the donor's blood. The most frequent blood transfusion reactions are caused by substances of the ABO blood group blood groups, differentiation of blood by type, classified according to immunological (antigenic) properties, which are determined by specific substances on the surface of red blood cells.
..... Click the link for more information. system and the Rh factor Rh factor, protein substance present in the red blood cells of most people, capable of inducing intense antigenic reactions. The Rh, or rhesus, factor was discovered in 1940 by K. Landsteiner and A. S.
..... Click the link for more information. system. In the ABO system, group AB individuals are known as universal recipients, because they can accept A, B, AB, or O donor blood. Persons with O blood are sometimes called universal donors, since their red cells are unlikely to be agglutinated by the blood of any other group. In the Rh factor system, agglutinins are not produced spontaneously in an individual but only in response to previous exposure to Rh antigens, as in some earlier transfusion. Transfusion reactions involving incompatibility eventually cause hemolysis, or disruption of donor cells. The resulting liberation of hemoglobin into the circulatory system, causing jaundice and kidney damage, can be lethal.

In addition to providing for the compatibility of blood groups in transfusion, it is necessary to determine that the donor's blood is free of organisms that might cause syphilis syphilis (sĭf`əlĭs), contagious sexually transmitted disease caused by the spirochete Treponema pallidum
..... Click the link for more information. , malaria malaria, infectious parasitic disease that can be either acute or chronic and is frequently recurrent. Malaria is common in Africa, Central and South America, the Mediterranean countries, Asia, and many of the Pacific islands.
..... Click the link for more information. , serum hepatitis Hepatitis A, also called infectious hepatitis, occurs sporadically or in epidemics, the virus being present in feces and transmittable via contaminated food (e.g., food prepared by an infected person with unwashed hands or fresh food washed or grown with contaminated water) or
..... Click the link for more information. , or HIV HIV (Human Immunodeficiency Virus), either of two closely related retroviruses that invade T-helper lymphocytes and are responsible for AIDS . There are two types of HIV: HIV-1 and HIV-2. HIV-1 is responsible for the vast majority of AIDS in the United States.
..... Click the link for more information. , the virus believed to cause AIDS AIDS or acquired immunodeficiency syndrome, fatal disease caused by a rapidly mutating retrovirus that attacks the immune system and leaves the victim vulnerable to infections, malignancies, and neurological disorders.
..... Click the link for more information. . Allergic reactions to transfusions may occur in cases where allergic antibodies have been transmitted from the donor's blood, possibly because of some type of food recently ingested by the donor. These problems have increased the popularity of autologous transfusions, transfusions using a person's own blood, which has been donated ahead of time. See blood bank blood bank, site or mobile unit for collecting, processing, typing, and storing whole blood , blood plasma and other blood constituents. Most hospitals maintain their own blood reserves, and the American Red Cross provides a nationwide collection and distribution
..... Click the link for more information. .

blood transfusion

Transfer of blood taken from one person into the circulation of another to restore blood volume, increase hemoglobin levels, or combat shock. Once the blood-group antigens and antibodies (see ABO blood-group system, Rh blood-group system) were discovered, blood typing of donors and recipients rendered transfusion safe. In exchange transfusion, all or most of the blood is removed and replaced with another's blood. Undesirable reactions to transfusion are not uncommon.