Pinworm Test

Picture of pinworm and pinworm eggs (magnified). Source: CDC.gov

Pinworm infection is caused by the helminth (Enterobius vermicularis), a small, white parasitic worm. The pinworm is about the length of a staple (ranges from 2 to 13 mm [0.08 to 0.5 inches]) and lives for the most part in the rectum of humans. While an infected person is asleep, female pinworms exit the intestines through the anus and deposit eggs on the skin around the anus. Within a few hours of being deposited on the skin around the anus, pinworm eggs become infectious (capable of infecting another person). Pinworm eggs can survive up to three weeks on clothing, bedding, or other objects if the environment is sufficiently moist.

If pinworms are suspected, transparent adhesive tape or a pinworm paddle (supplied by your healthcare provider) is applied to the anal region. The tape can pick up both eggs and occasionally the adult worms. Most clinicians suggest the test be done as soon as the person awakens and before any bowel movement or cleansing (bath, shower) as these actions tend to remove the eggs and parasites from the anal/rectal area.

The pinworm eggs or a few adult worms adhere to the sticky tape or paddle and are identified by examination under an ordinary microscope by a qualified laboratory technician.

In some individuals, it is possible to see the adult worms without a microscope, but the transparent eggs are small and can only be seen with a microscope.

The test should be done as soon as you wake up in the morning (because bathing or having a bowel movement may remove eggs). The exam may require several samples for a positive diagnosis. Researchers suggest that repeating the test at about three different intervals yields about a 90% detection rate.

Samples taken from under the fingernails may also contain eggs (since scratching of the anal area is common).

At night, the adult worms can sometimes be seen directly on the bedclothes or around the anal area. The best time for observation is at night when itching in the anal/rectal area awakens a person; it is likely the sensation caused by migrating female worms depositing eggs and irritating the skin (see the following section).

The pinworms are white, can be seen with the naked eye (no magnification) and are about the length of a staple (about 8-13 mm for female and 2-5mm for male worms). The eggs that are laid by the female worms are not visible as they are about 55 micrometers in diameter and are translucent (see Figure 1).

The male and female worms live for the most part within the rectum of humans but have a life cycle in humans that involves rectal/oral transmission (see Figure 2).

Picture of the life cycle of a pinworm. Source: CDC.gov

While an infected person is asleep, female pinworms leave the intestines through the anus and deposit eggs on the skin around the anus. This causes itching and irritation of the surrounding area; children especially will scratch the rectal/anal area, get eggs on their fingers or underneath their fingernails and transport the infective eggs to bedding, toys, other humans, or back to themselves. The eggs hatch into larval forms in the small intestines and then progress to the large intestine where they mature, mate, and progress to the rectal/anal area where females deposit about 10 to 15 thousand eggs.