Blood Typing

Test Description

The foundation of blood typing is the detection of ABO and Rh antigens on the red
blood cells of an individual’s blood. Each person has one blood type (A, B, AB, or O)
which is genetically determined. These blood type designations specify the antigen
present on the person’s red blood cells. For example, a person with type B blood has
the B antigen on the red blood cells, and someone with type O blood has no antigens
Another important aspect of blood typing is understanding the presence of antibodies
in the blood and what they mean to blood transfusion therapy. In order for
someone to receive blood from a donor with a minimum of risk for a transfusion
reaction, the donor’s blood must have no antibodies against the recipient’s red
blood cells, and the recipient’s blood must have no antibodies against the donor’s
red blood cells. For example, a person with type AB blood has no antibodies present
and can therefore theoretically receive blood of any of the four blood types
(A, B, AB, or O). Thus a person with type AB blood is often called the “universal
recipient”. A person with type O blood, on the other hand, has both anti-A and anti-
B antibodies and can therefore receive only type O blood, the only type with no antigen
on its red blood cells. Individuals with type O blood are referred as “universal
donors”, because their blood, which has no antigens present on the red blood cells,
will theoretically cause no reaction when administered to any of the four blood types.
The blood types with their associated antigens and antibodies, and a synopsis
of donor and recipient blood types is summarized in Table B-1. Please note that
although several blood types may be listed as being appropriate for use in a transfusion
for a particular blood type, this applies to small volumes of blood being
received. However, when large volumes of whole blood are transfused, ABO matching
is essential.

Another component of blood typing is that of Rh-typing. Rh factor, also known
as D factor, was so named because the rhesus monkey was used in the initial investigations
into this factor. An individual is either Rh-positive or Rh-negative. The
Rh-positive individual has the Rh antigen present on the red blood cells and no antibodies
against the Rh factor. The Rh-negative individual has no antigens present on
the red blood cells and has anti-Rh antibodies if previously sensitized by Rh-positive
blood. In Rh-negative males, this sensitization would have occurred through transfusion
with Rh-positive blood. In Rh-negative females, the sensitization could have
occurred either through transfusion with Rh-positive blood, or through pregnancy in
which the fetus was Rh-positive.
Determination of the Rh-factor is crucial for pregnant women. If the woman is
Rh-negative and her partner’s blood is Rh-positive, the fetus is Rh-positive. If the
woman is Rh-negative, an indirect Coombs’ test, which screens for Rh antibodies,
is ordered. If the test is positive, Rh antibodies are present and Rh antibody titers
are then obtained. If the antibody test is negative both initially and again late in the
pregnancy, there is no risk to the fetus. If, however, the test is positive, the Rhnegative
mother is producing antibodies against the red blood cells of the Rhpositive
fetus. These antibodies may cross the placenta and cause destruction of
fetal red blood cells before or during birth. This results in a hemolytic disease
known as hemolytic disease of the newborn or erythroblastosis fetalis. This disease can
be prevented by administering an anti-Rh antibody preparation (RhoGAM) in the
third trimester of pregnancy to women at risk.
RhoGAM acts to suppress the mother’s production of antibodies in response to
receiving the Rh-positive antigen. RhoGAM should be given to all Rh-negative
women whenever there is a possibility of fetal-maternal transplacental hemorrhage,
no matter how minor. Such hemorrhage may occur as a result of chorionic villus
sampling, amniocentesis, spontaneous or therapeutic abortion, or delivery.
When a person receives an incompatible type of blood, that person’s antibodies
attack the antigens present on the red blood cells of the donor blood. For example,
a person with Type A blood has anti-B antibodies present in the blood. If this person
is given type B blood, which has B antigens on the red blood cells, the recipient’s
anti-B antibodies will attack the donor’s B antigens, resulting in a hemolytic,
or transfusion reaction. Such a reaction can result in renal failure and death of the
recipient. To avoid the occurrence of transfusion reactions, testing of both the recipient’s
blood and the donor’s blood is done in order to ensure compatibility. Two tests
which are conducted are the “type and crossmatch” and the “type and screen”.
The type and crossmatch testing includes several components which take approximately
an hour to complete. First, the ABO group and Rh-type of the recipient are
determined. Next, from the donated blood supply available, donor blood of the
same ABO group and Rh-type is chosen for compatibility testing. Indirect Coombs’
testing, which is a general screening for antibodies, is performed on both the recipient
and donor blood. More specific antibody testing may be required to identify
unusual antibodies. Once these tests are completed, samples of the recipient’s
blood and the donor’s blood are combined (crossmatched). If no antigen-antibody
reaction occurs, the donor blood is considered to be compatible, and thus acceptable
for transfusion into the recipient.
Type and screen testing includes only testing to determine the ABO group and
Rh-type and the indirect Coombs’ test. Actual crossmatching with donor blood is
not performed. Type and screen testing is conducted in situations in which there is
only a slight chance of the person requiring blood, or in emergency situations.

THE EVIDENCE FOR PRACTICE

The U.S. Preventive Services Task Force (USPSTF) strongly recommends Rh(D) blood
typing and antibody testing for all pregnant women during their first visit for pregnancyrelated
care. The USPSTF found good evidence that Rh(D) blood typing, anti-Rh(D) antibody
testing, and intervention with Rh(D) immunoglobulin, as appropriate, prevents maternal
sensitization and improves outcomes for newborns.
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Normal Values

Compatible (no antigen-antibody reactions between donor and recipient blood samples)

Contributing Factors to Abnormal Values

• Hemolysis of the blood sample may alter test results.
• Administration of Dextran or IV contrast media prior to the test may alter test results.
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Interventions/Implications

Pretest

• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.
• No fasting is required prior to the test.
• The blood sample should be drawn before administration of Dextran, a plasma volume
expander.

Procedure

• A 10-mL blood sample is drawn in a lavender-top (EDTA) collection tube.
• Gloves are worn throughout the procedure.

Posttest

• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued
bleeding.
• Label the specimen and transport it to the laboratory.
• Report ABO group and Rh type to the primary care provider.
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Clinical alert             
•• Avoidance of errors is essential. Typically when blood is drawn for a type and crossmatch,
a blood bank identification band is applied to the patient’s wrist. This
band can be compared to blood products to be administered to the patient.
• Follow institutional policy regarding identification of the patient prior to blood
administration. Typically two health-care providers must verify that the blood
group and Rh type of the recipient and donor are compatible and that the proper
unit of blood is being used prior to blood administration.