blood group

A genetically determined system of antigens located on the surface of the erythrocyte. There are a number of human blood group systems, each determined by a series of two or more genes that are allelic or closely linked on a single autosomal chromosome. The ABO system is important in blood transfusions. The Rhesus (Rh) system is important in obstetrics (there are about 30 Rh antigens).

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ABO BLOOD TYPES ; SEE: histo-blood group antigen; SEE: Rh factor
The population can be phenotypically divided into four ABO blood groups: A, B, AB, and O. Those in the A group have the A antigen on the surface of their red cells; the B group has the B antigen on red cells; the AB group has A and B antigens on red cells; and the O group has neither A nor B antigens on red cells. Those people in each group have in their sera the corresponding antibody to the red cell antigens that they lack. Thus, a person in group A has the anti-B antibody; group B has anti-A antibodies; group AB has no antibodies for A and B; and those in group O have anti-A and anti-B antibodies in their sera.

Blood group factors are important in blood banking. Analysis of blood groups is important in identification of bloodstains for medicolegal purposes, in genetic and anthropological studies, and, formerly, in determination of the probability of fatherhood in paternity suits.

Video for blood type and transfusion reactions

Hh blood group

A blood group rare in Western populations, found most often in those of Taiwanese or Indian descent, and determined by a particular oligosaccharide on the surface of red blood cells. The absence of the H antigen (the determining oligosaccharide of this blood group) can result rarely in severe transfusion reactions when an H-deficient person receives blood from any ABO blood group donor.

Kell blood group

SEE: Kell blood group

Rh blood group

A group of antigens on the surface of red blood cells present to a variable degree in human populations. When the Rh factor (an antigen often called D) is present, a person's blood type is designated Rh+ (Rh positive); when the Rh antigen is absent, the blood type is Rh− (Rh negative). If someone with Rh- blood receives a transfusion of Rh+ blood, anti-Rh antibodies form. Subsequent transfusions of Rh+ blood may result in serious transfusion reactions (agglutination and hemolysis of red blood cells). A pregnant woman who is Rh- may become sensitized by entry of red blood cells from an Rh+ fetus into the maternal circulation after abortion, ectopic pregnancy, or delivery. In subsequent pregnancies, if the fetus is Rh+, Rh antibodies produced in maternal blood may cross the placenta and destroy fetal cells, causing erythroblastosis fetalis.
SEE: Rh immune globulin