Question
NIH swab
Answer
The NIH (National Institutes of Health) swab, also called the perianal (Scotch/cellophane tape) swab, is a specific specimen-collection technique used for the diagnosis of enterobiasis (pinworm infection, Enterobius vermicularis).
Principle: the gravid female pinworm migrates out through the anus at night to lay her eggs on the perianal skin, rather than depositing eggs within the intestinal lumen — as a result, Enterobius eggs are typically absent from routine stool samples, making a perianal swab (rather than stool examination) the specimen of choice for diagnosis.
Procedure: the sticky side of a strip of clear adhesive (cellophane) tape (or a specifically designed NIH swab/paddle) is pressed firmly against the perianal skin folds, early in the morning, before the child bathes or defecates (since overnight-deposited eggs would otherwise be washed away or disturbed); the tape/swab is then applied directly onto a glass slide (sticky side down) for microscopic examination.
Microscopy findings: characteristic Enterobius vermicularis eggs — asymmetrically oval, flattened on one side (“D-shaped”), thin-shelled, colourless, typically containing a fully developed larva.
Practical notes: since egg deposition is intermittent (not every night), repeated sampling on 2–3 consecutive mornings significantly improves diagnostic sensitivity compared to a single swab; the technique is simple, painless, and can be performed by parents at home with appropriate instruction before sample transport to the laboratory.