does o negative blood exist

Blood type - Wikipedia, the free encyclopedia


** Blood type **

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Blood type (or blood group) is determined, in part, by the ABO blood group
antigens present on red blood cells.

A *blood type* (also called a *blood group*) is a classification of blood
based on the presence or absence of inherited antigenic substances on the
surface of red blood cells (RBCs). These antigens may be proteins,
carbohydrates, glycoproteins, or glycolipids, depending on the blood group
system. Some of these antigens are also present on the surface of other
types of cells of various tissues. Several of these red blood cell surface
antigens can stem from one allele (or an alternative version of a gene) and
collectively form a blood group system.^[1] Blood types are inherited and
represent contributions from both parents. A total of 35 human blood group
systems are now recognized by the International Society of Blood
Transfusion (ISBT).^[2] The two most important ones are ABO and the RhD
antigen; they determine someone's blood type (A, B, AB and O, with +,
− or Null denoting RhD status).

Many pregnant women carry a fetus with a blood type which is different from
their own, which is not a problem. What can matter is whether the baby is
RhD positive or negative. Mothers who are RhD- and carry a RhD+ baby can
form antibodies against fetal RBCs. Sometimes these maternal antibodies are
IgG, a small immunoglobulin, which can cross the placenta and cause
hemolysis of fetal RBCs, which in turn can lead to hemolytic disease of the
newborn called erythroblastosis fetalis, an illness of low fetal blood
counts that ranges from mild to severe. Sometimes this is lethal for the
fetus; in these cases it is called


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