CLINICAL LAB SCIENEC

338
ESSENTIALS OF CLINICAL LABORATORY SCIENCE
In the Lab
Smear
too thin
Proper area of
smear to view cells
Smear
too thick
Area of smear
where cells do
not overlap
Serpentine
counting
pattern
FIGURE 13-7 Finding the proper area of the slide for evaluating red
blood cell morphology and counting white blood cells accurately.
Source: Delmar/Cengage Learning.
11. Adjust the condenser and the iris diaphragm
until a good image of the cells is obtained.
12. Scan the slide from side to side, making
sure the focal field is in an area where
the cells are not touching. Move the slide
along the stage of the microscope in a
broad lane running transversely across the
body of the film, avoiding the edges completely
(Figure 13-7), as cells are sometimes
dragged there in greater numbers.
13. Count 100 or 200 cells.
a. Use the 40 objective high-power lens
to perform a 200 cell count. (The 100
objective oil immersion lens should be
reserved for examining fine intracellular
details and when searching for parasites
inside the cells.)
b. Count in multiples of 100 so that you can
later calculate the percentage of the
various cell types.
c. Take your time! Count 200 cells to be
sure of your results. You should refer to
Figure 13-6 to help differentiate the various
types of cells.
d. If 200 WBCs are counted, the total of
each type is divided by 2 to obtain a percentage.
Some differential counters will
perform this task for you.
14. Record the numbers of each type of WBC counted on the report form. If available
to you, use a mechanical or electronic differential counter.
15. Remember that the technical laboratory professional should not merely focus on
WBCs. RBC evaluation will be covered in Procedure #5. The experienced laboratory
professional may assess both WBCs and RBCs simultaneously.
16. Observe at least 10 fields for platelet evaluation under oil immersion (1000X).
Observe for size and morphology (shape). Estimate the approximate platelet
count by taking the total platelets appearing in 10 fields, and divide by 10 to obtain
the average number per microscopic field. Platelets are reported as adequate,
increased, or decreased. Record the information on the report form.
17. Return the low-power objective (10X) into place and remove the slide from the
stage.
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