|
The Rh blood group system (including the Rh factor) is one of thirty-five current human blood group systems. It is the most important blood group system after ABO. At present, the Rh blood group system consists of 50 defined blood-group antigens, among which the five antigens D, C, c, E, and e are the most important. The commonly used terms ''Rh factor'', '' Rh positive'' and ''Rh negative'' refer to the ''D antigen'' only. Besides its role in blood transfusion, the Rh blood group system—specifically, the D antigen—is used to determine the risk of hemolytic disease of the newborn (or erythroblastosis fetalis) as prevention is the best approach to the management of this condition. As part of prenatal care, a blood test may be used to find out the blood type of a fetus. If the Rh antigen is lacking, the blood is called Rh-negative. If the antigen is present, it is called Rh-positive. When the mother is Rh-negative and the father is Rh-positive, the fetus can inherit the Rh factor from the father. This makes the fetus Rh-positive too. Problems can arise when the fetus’s blood has the Rh factor and the mother’s blood does not. A mother who is Rh-negative may develop antibodies to an Rh-positive baby. If a small amount of the baby’s blood mixes with the mother’s blood, which often happens in such situations, the mother’s body may respond as if it were allergic to the baby. The mother’s body may make antibodies to the Rh antigens in the baby’s blood. This means the mother has become sensitized and her antibodies may cross the placenta and attack the baby’s blood. Such an attack breaks down the fetus’s red blood cells, creating anemia (a low number of red blood cells). This condition is called hemolytic disease or hemolytic anemia. It can become severe enough to cause serious illness, brain damage, or even death in the fetus or newborn. Sensitization can occur any time the fetus’s blood mixes with the mother’s blood. It can occur if an Rh-negative woman has had a spontaneous or undetected miscarriage of a Rh positive fetus. ==Rh factor== An individual either has, or does not have, the "''Rh factor''" on the surface of their red blood cells. This term strictly refers only to the most immunogenic D antigen of the Rh blood group system, or the Rh− blood group system. The status is usually indicated by ''Rh positive'' (Rh+ does have the D antigen) or ''Rh negative'' (Rh− does not have the D antigen) suffix to the ABO blood type. However, other antigens of this blood group system are also clinically relevant. These antigens are listed separately (''see below: Rh nomenclature''). In contrast to the ABO blood group, immunization against Rh can generally only occur through blood transfusion or placental exposure during pregnancy in women. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rh blood group system」の詳細全文を読む スポンサード リンク
|