- Author: Sun Huh, MD, PhD; Chief Editor: Michael Stuart Bronze, MD more...
Glass slide microscopic analysis for Enterobius vermicularis may be performed looking for ova and female pinworms. A specimen is best obtained by dabbing the stretched, unwashed perianal folds in the early morning with cellophane tape and affixing the specimen onto a slide. A negative test for 5 consecutive mornings effectively rules out the diagnosis.
Microscopic examination shows the elongated ovoid egg distinctly compressed laterally and flattened on one side. The egg measures 50-60 µm X 20-30 µm and contains larva.
In areas where pinworms are endemic, consider analyzing any removed appendiceal stump for infestation.
Patients with recurrent episodes of perianal itching should have a stool sample sent to the laboratory for analysis because different parasites, which require different treatment, may appear similar to E vermicularis using the cellophane-tape test.
A perianal cellophane swab or cellophane-tape examination should be used to detect Enterobius vermicularis eggs (see the image below). Egg detection is associated with false-positive rate of 5-11% and a false-negative rate of 70-95%. One report found that a single cellophane-tape examination yielded a sensitivity of 50%, 3 examinations yielded a sensitivity of 90%, and 5 examinations yielded a sensitivity of 99%.
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