Hemolytic Disease of a Newborn
is Due to an Rh incompatibility
The Rh blood antigen can cause problems during preg-
nancy if the mother is Rh-negative (see Figure
10.8c).
(Rh-positive mothers do not need to be concerned about
this condition.) If an Rh-negative mother gives birth to an
Rh-positive baby, some of the baby’s blood can move into
the mother’s blood during the birth process. The mother’s
body responds to this foreign antigen by creating anti-Rh
antibodies. Although the recently delivered baby will be un-
affected, subsequent pregnancies involving an Rh+ infant
can be affected. During a subsequent pregnancy, these an-
tibodies can cross over the placenta and get into the baby’s
circulation, causing incompatibility and damage to the ba-
by’s RBCs—a condition known as hemolytic disease of the
newborn. This condition can be prevented by injecting the
mother with anti-Rh antibodies after delivery of the first
baby and during the pregnancy and delivery of subsequent
children. These antibodies destroy any Rh antigens that
manage to get into the mother’s circulation and prevent the
mother from developing anti-Rh antibodies. (See Chapter
12 for more about immunity.) Without anti-Rh antibodies
in the mother’s system, no antibody is passed to the future
babies, and hemolytic disease of the newborn will not occur.
CONCEPT CHECK
1.
What
antigen(s) does a person with type
B-positive blood have on her RBCs?
2.
H
ow
does hemolytic disease of the newborn
occur?
3.
Which
blood types are compatible with type O?
Analysis of Blood Components Can Tell Much
About an Individual's Health
l e a r n in g
o b je c t iv e s
1.
Identify
the locations in the body where you
can obtain blood samples.
2.
Describe
what is measured in blood tests,
including hematocrit, reticulocyte count, differ-
ential WBC count, and complete blood count.
3.
Explain
the condition(s) each blood test might
indicate.
ecause the composition of blood at any given
time can be an indicator of good health or
disease, blood tests are common in clinical
settings. Blood samples can be taken from
multiple places, and common blood tests can be run for
diagnostic purposes.
Blood for Testing Can Be
Obtained in Several Ways
The first step in any blood test is to obtain a sample of
blood. A test may require only a drop or two of blood (as in
blood typing), or it may require volumes as large as one or
more 5-10 mL tubes (as in measuring various chemicals
in blood). Blood samples can usually be obtained by one of
the following methods:
F in g erstick
—A sterile needle or lancet is used to prick a
finger, an earlobe, or a heel to obtain a drop or two of
capillary blood.
V enipuncture
—A sterile needle and syringe can puncture
a surface vein, usually the median cubital vein in front
of the elbow. A tourniquet is used to stop the blood
flow from the veins and makes them easier to see. This
method is used to obtain several milliliters of blood.
A rte ria l stick
—A sterile needle and syringe are used to
sample blood from an artery, usually the radial artery
at the wrist or the femoral artery at the thigh. Like
venipuncture, this method is used to obtain several
milliliters of blood.
Depending on the type of tests that will be done, the
blood will either be maintained in a fluid form or will
be allowed to clot. Tests that are evaluating the formed
elements or the clotting capability of the blood require
the blood to be in a fluid form. Tests that are determin-
ing the chemical composition of the blood work with the
liquid component and may require either fluid blood or
clotted blood.
Analysis of Blood Components Can Tell Much About an individual's Health 299
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