Blood Chemical Composition Testing
uses Either plasma or Serum
The liquid used for blood chemical composition tests is re-
ferred to either as
p la sm a
or
serum ,
depending on how the
sample is collected. Plasma is extracted from blood that is
still in a fluid form. In the blood vessels, the blood remains
in fluid form because it is constantly moving. To keep blood
in a fluid form after it is removed from the body, the collec-
tion tube must contain
a n tic o a g u la n t
chemicals.
If blood removed from the body is not stored with anti-
coagulants, the blood will quickly solidify (clot). The liquid
in a blood sample that has clotted is called serum. Serum
is quite similar in composition to plasma but is missing one
of the proteins (fibrinogen) found in plasma. Extracting the
liquid from the blood, whether fluid or clotted, requires that
the tube be spun in a centrifuge. As we mentioned before,
cells fall to the bottom, and the plasma or serum ends up at
the top of the tube (see Figure 10.1).
Blood tests Are Often used
to Diagnose Disease
Once a blood sample has been collected, it can be used
for a number of different tests that study the formed ele-
ments of the blood. These tests include the hematocrit,
reticulocyte count, differential white blood cell count,
and/or
complete
blood
count
(Figure 10.9). These tests can
provide a wide range of informa-
tion regarding blood conditions,
such as the following:
1. Polycythemia
. Too many RBCs
(or
p o lycyth em ia vera,
too many
formed elements of all types).
2. Anemia
due to too few RBCs:
P ernicious a n em ia .
Insufficient
hemopoiesis
H em o rrh a gic a n em ia .
Excessive loss of blood through
bleeding
resulting
from
large
wounds,
stomach
ulcers, or especially heavy menstruation.
H em o lytic a n em ia .
Premature rupture of RBC plasma
membranes; may be caused by inherited defects
or by outside agents such as parasites, toxins, or
antibodies from transfused blood.
A p la s tic a n em ia .
Destruction of red bone marrow due
to toxins, gamma radiation, and certain medications
polycythemia
(pol'-e-sr-THE-me-a) A
disorder characterized
by an above-normal he-
matocrit (above 55%).
anemia
(a-NE-me-a)
A condition of the
blood in which the
number of functional
red blood cells or their
hemoglobin content is
below normal.
3.
Anemia due to deficiency of functional hemoglobin in
each RBC:
Iron-deficiency a n em ia .
Inadequate intake or absorption
of iron or excessive loss of iron (This is the most
common type of anemia.) Women are at greater risk
for this type of anemia because of monthly menstrual
blood loss.
S ic k le cell a n em ia .
Genetic disorder
in which a defective hemoglobin is
ue
J
formed in the RBC. (This abnormal
hemoglobin causes the RBCs to form a
crescent
shape, which rupture easily. Even though the loss of
RBCs stimulates erythropoiesis, it cannot keep pace
with hemolysis.)
T h a la ssem ia .
A group of hereditary hemolytic anemias
in which there is an abnormality in one or more of the
four polypeptide chains of the hemoglobin molecule.
Thalassemia occurs primarily in populations from
countries bordering the Mediterranean Sea.
4.
Leukemia
. Red bone marrow
cancers
in
which
abnormal
white
blood
cells
multiply
uncontrollably.
5.
Infections. Can be bacterial,
fungal, viral, or parasitic.
leukemia
(loo-KE-
me-a) A malignant
disease of the blood-
forming tissues.
Plasma samples can be used to determine the pa-
tient’s ability to clot the blood effectively. A variety of
tests using serum can also be done to study the chemi-
cal composition of the blood. These tests can determine
such things as the level of various metabolites that may
be present in the blood, including glucose, cholesterol,
urea, and enzymes. Such tests can determine whether in-
ternal organs are functioning correctly or whether there
are abnormal levels of electrolytes and waste materials
that could impact body organs. Because the blood is such
an important transport medium, it can serve as a “win-
dow” to your health.
CONCEPT CHECK
1.
Which
part of the body would you most likely
use to get a few drops of blood?
2.
What
does a hematocrit measure?
3.
Which
blood test would be the most helpful in
determining whether a patient has an infection?
300 CHAPTER 10
The Cardiovascular System: Blood
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