Download Differential WBC count lab

Anatomy & Physiology
A White Blood Cell Study: The Differential WBC Count
The blood is an opaque, rather viscous fluid that is bright red when
oxygenated and dark red when depleted of oxygen. Its specific gravity is
normally 1.06 and its pH is slightly alkaline (pH > 7). When centrifuged,
blood becomes separated into a dark red portion made up of formed
elements and a clear straw-colored portion called plasma. The formed
element content of blood is around 47% in men and 42% in women.
During this lab exercise, you will study the leukocytic portion of the
formed elements in blood. This study will involve prepared blood slides.
The formed elements of blood consist of erythrocytes (red blood
cells), leukocytes (white blood cells), and blood platelets. Erythrocytes are
non-nucleated cells with depressed centers that contain hemoglobin. (Their
shape resembles the Werther's caramel candy)
RBCs are the most
numerous element in blood - around 4.5 to 5.5 million cells per cubic
millimeter!!
The leukocytes are of two types: granulocytes and agranulocytes. The
granulocytes are so named because they have conspicuous granules in their
cytoplasm. Neutrophils, eosinophils, and basophils fall into this category.
The agranulocytes
lack pronounced granules in the cytoplasm; the
monocytes and lymphocytes are of this type.
The blood platelets are noncellular elements in the blood that assist in
the clotting process.
In this lab exercise, the formed elements will be examined in an
attempt to determine the percentage of each type of leukocyte on a slide.
By scanning an entire slide and counting the various types, you will have an
opportunity to encounter most, if not all, types. The erythrocytes and blood
platelets will be ignored. The main purpose of this exercise will be to learn
how to distinguish the various types of white blood cells, not to become
proficient in performing differential WBC counts.
The normal percentage ranges for the various leukocytes are as
follows:
Neutrophils
Lymphocytes
Monocytes
Eosinophils
50-70%
20-30%
2-6%
1-5%
Basophils
0.5 - 1%
"Never Let Monkeys Eat Bananas" is an easy pneumonic device to help you
remember the relative abundance of each type of leukocyte.
** Because of the extremely low percentages of eosinophils and basophils, it
is necessary to examine at least 100 leukocytes to increase the possibility of
encountering one or two of them on a slide.
Deviations from the above percentages may indicate serious
pathological conditions. High neutrophil counts, or neutrophilia, often signal
localized infections such as appendicitis or abscesses in some part of the
body. Neutropenia, a condition in which their is a marked decrease in the
number of neutrophils, occurs in typhoid fever, undulant fever, and
influenza.
Eosinophilia (high eosinophil count) may indicate allergic
conditions or invasions by parasitic roundworms such as Trichinell spiralis,
the pork worm (be sure to thoroughly cook all pork products!!!) Counts of
eosinophils may rise to as much as 50% of the total leukocytes in cases of
trichinosis. High lymphocyte counts (> 10,000 per cubic millimeter), or
lymphocytosis, are present in whooping cough and some viral infections. A
total WBC count below 5,000 per mm3 of blood is called leukopenia (a form
of neutropenia) and may indicate the conditions of AIDS, measles, mumps, or
chicken pox.
A white cell count that determines the relative percentages of each
type of leukocyte is called a differential white blood cell count. It is this
type of a count that will be performed here.
PROCEDURES:
1.
Obtain a prepared blood slide. You will notice that the slide may be
titled "Wright's Stain" - this is only to indicate what type of stain was
used in preparing the slide.
2.
Scan the slide with the low-power objective to find an area where cell
distribution is best. A good area is one in which the cells are not
jammed together or scattered too far apart.
3.
Once an ideal area has been selected, switch to the high-power
objective.
4.
Systematically scan the slide, following a path going down, across, up,
across, down, etc... As each leukocyte is encountered, identify it using
your notes, text book, or histology atlas for assistance.
5.
Neatly tabulate your count in a data table and include with your review
questions.
6.
Examine and perform a differential WBC count on a prepared slide of
mononucleosis or leukemia. Include your results in your data table.
REVIEW QUESTIONS: (Answer on a separate sheet of paper)
1.
Include a detailed sketch of each of the five types of white blood
cells. Describe the function of each type of leukocyte under your
sketch.
2.
A normal red blood cell count for males is around 5,400,000 cells per
mm3 and aroiund 4,600,000 cells per mm3 for women. What is the
function of the RBC, and why do indigenous people of the himalayas
have a RBC higher than average?
3.
Why would an elevated WBC count indicate a potential health
problem?
4.
If a patient with an inoperable cancer takes a drug that reduces the
rate of cell division, how might the patient's WBC count change? How
could the patient's environment be modified to compensate for the
effects of these changes?
5.
What is erythropoietin? A synthetic form is available as a drug - why
would athletes abuse it?