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Laboratory Procedures for Identifying Parasitic Organisms and Their Ova 277

Equipment and Supplies
1. Protective gloves and disposable gown
2. Wright-Giemsa Stain (Quick-Stain)
3. Absolute Methanol (methyl alcohol)
4. Distilled water
5. 3 Coplin jars or equivalent containers
6. 1 mL disposable pipet
7. Known positive controls slides are optional but important
8. Microscope slides
Procedural Steps
Most likely malarial parasite stages will be observed on the thick smears, and

identification will be definitive from the stained thin smears.
Preparing the Slides (Thick and Thin)
1. Prepare both thin and thick smears (see Figures 12-9–12-11). Thick films must

not be extremely thick as they will peel from the slide. The ability to barely
discern newsprint with the initial wet drop for the thick film is optimum.

2. Use clean microscopic slides only. For thick smears, place six drops of blood
on the slide, two each in the three points of triangular shape (see Figure 12-10).
Use the corner of another slide to mix the drops in a circular motion and spread
them out to the approximate size of a dime. Allow the slide to air dry for 6 to
8 hours, preferably over night. Thin smears are made in the same manner as
those for a routine blood smear performed during a complete blood count.

Clinical Precaution:
Only air-dry the thick smears. Do not heat the thick smears with a flame or slide

warmer; this tends to fix the RBCs. Recall that methanol as a fixative will prevent

the RBCs from lysing when water is added to the thick drops.

Delmar/Cengage Learning

FIGURE 12-9 Preparing a thin blood smear for examination for parasites
(continues)