Blood Type Test
Type O-negative blood does not have any antigens. It is called the
"universal donor" type because it is compatible with any blood type. Type
AB-positive blood is called the "universal recipient" type because a person who
has it can receive blood of any type. Although "universal donor" and "universal
recipient" types may be used to classify blood in an emergency, blood type
tests are always done to prevent transfusion reactions.
antigens (other than A, B, and Rh) that occur on red blood cells can sometimes
also cause problems and so are also checked for a match before giving a blood
Serious transfusion reactions are rare today because
of blood type tests.
Rh blood type checks for the Rh antigen
(also called the Rh factor) on red blood cells. If your red blood cells:
- Have the Rh antigen, your blood is
- Do not have the Rh antigen, your blood is
For example, if you have the A and Rh antigens, your
blood type is A-positive (A+). If your blood has the B antigen but not the Rh
antigen, your blood type is B-negative (B–).
Rh blood type is
especially important for pregnant women. A problem can occur when a woman who
has Rh-negative blood becomes pregnant with a baby (fetus) that has
Rh-positive blood. This is called Rh incompatibility. If the blood of an
Rh-positive baby mixes with the blood of an Rh-negative mother during pregnancy
or delivery, the mother's immune system makes antibodies. This antibody
response is called
Rh sensitization and, depending on when it occurs, can
destroy the baby's red blood cells.
Rh sensitization does not
generally affect the health of the baby during the pregnancy in which the
sensitization occurs. But the health of a baby with Rh-positive blood during a
future pregnancy is more likely to be affected. After sensitization has
occurred, the baby can develop mild to severe problems (called Rh disease or
erythroblastosis fetalis). In rare cases, if Rh
disease is not treated, the baby may die.
An Rh test is done in
early pregnancy to check a woman's blood type. If she is Rh-negative, she can
get a shot of
Rh immunoglobulin that almost always prevents sensitization from occurring.
Problems from Rh sensitization have become very rare since Rh immunoglobulin