Enterobiasis laboratory findings

Diagnosis of enterobiasis is often made clinically by observing the female worm(s) in the peri-anal region, but can also be made using the “scotch-tape” test, in which the sticky side of a strip of cellophane tape is pressed against the peri-anal skin, then examined under a microscope for pinworm eggs.

It is also called Hall or National Institute of Health swab. Sticky side of a strip of cellophane tape is pressed against the peri-anal skin, then examined under a microscope for pinworm eggs. The test is repeated for five consecutive mornings to increase the sensitivity to 99%. It is done prior to washing or defecation. The diagnostic characteristics of egg are: size 50-54 µm by 20-27 µm; typical elongated shape, with one convex side and one flattened side and colorless shell.^[1][2]

Stool analysis for ova and parasites is of low diagnostic yield. The actual worms may be seen in the host’s feces; however the eggs are invisible to the naked eye.^[1]

On histologic cross-section alae or wings (running the length of the worm) are identifying features of the pinworm (see micrograph).^[3]

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  Two pinworms, captured on emergence from the anus. Markings are 1 mm apart.
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  Pinworms are sometimes diagnosed incidentally by pathology. Micrograph of pinworms in the appendix. H&E stain.
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  High magnification micrograph of a pinworm in cross-section in the appendix. H&E stain.
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  High magnification micrograph of a pinworm in cross-section in the appendix. H&E stain.
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  Enterobius vermicularis egg under a light microscope.
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  Pinworm eggs are easily seen under a microscope.
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  Pinworms are sometimes diagnosed incidentally by pathology. Micrograph of male pinworm in cross-section. Alae (blue arrow), intestine (red arrow) and testis (black arrow). H&E stain.
• 
  A pinworm (Enterobius vermicularis).

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