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Laboratory Procedures for Identifying Parasitic Organisms and Their Ova 281

QUALITY CONTROL MISCELLANEOUS METHODOLOGY
FOR RECOVERING SPECIFIC
As in all clinical laboratory procedures, quality con-
trol is paramount in order to provide accurate results. PARASITES
Commercial slides may be purchased and used to fa-
Several manual and commercial preparations are available
miliarize the learner or to enhance and challenge the
for convenient recovery of specific parasites from body
skills of experienced parasitologists, or permanent
sites of the human. Recovery of these organisms by the
slides from actual patient samples can be retained
methods described here are specific for a limited number
for review. Control samples may be preserved for ex-
of parasites. Some parasites do not lend themselves to
amination on a periodic basis to ensure stains are still
being easily isolated from fecal specimens, one of which
viable, or when new stains are prepared. WBCs from
is the common pinworm that infects many children. Oth-
a centrifuged, anticoagulated blood sample may be
ers that are not always found in the stool are recovered
incorporated into the control slides for comparison.
from certain body sites as is discussed in this section.
Control samples should be reviewed at least on a quar-
Many of the following collection techniques do not re-
terly basis and each time new stains are prepared. The
quire the care or elaborate preparations as the previous
ocular micrometer is initially calibrated for a particular
procedures do, so a step-by-step procedure is not neces-
microscope and should not be transferred to another
sary for each of these. Specimens gathered from the fol-
microscope due to individual differences between in-
lowing sources are directly examined by microscope and
struments. Recalibration should be performed on an
reported if found.
annual basis and anytime when doubt arises regarding
the accuracy of the calibration.
It is wise for those performing parasitology proce-
dures to maintain a familiarity with artifacts that may be Scotch Tape Prep for Pinworms
encountered when examining a wet mount. Many arti- Because pinworms and their ova are rarely recovered from
facts may be mistaken for parasites by the inexperienced stool specimens, a low-tech method that has been in exis-
or unwary laboratory technician. Artifacts include pol- tence for decades is described here. The life cycle of the
len or plant cells, WBCs and RBCs, yeasts, hair, starch pinworm called Enterobius vermicularis entails move-
granules, macrophages (large white cells), and mucosal ment from the colon to the anus, where the adult female
epithelium. Other areas of note are the presence of eo- lays eggs in the perianal area. Cellophane tape is used by
sinophils and Charcot-Leyden crystals associated with stretching a several inch strip over a tongue blade with
the breakdown of eosinophils, which are often found in the adhesive side to the outside of the tongue blade (see
heavy parasitic infections. Quality control results should Figure 12-13).
be recorded each time a procedure is performed and
out-of-control results should be accompanied by an ac-
tion plan that outlines the steps taken to determine the
cause for aberrations from the expected results.

Delmar/Cengage Learning

Slide with tape and label Lift tape and loop tape Replace tape after
over end of tongue depressor collecting specimen
to expose sticky surface

FIGURE 12-13 Cellophane tape/tongue blade device for recovering pinworm ova