The Entero-Test, also known as a duodenal capsule or string test, is used to retrieve parasites that inhabit the duodenal area. A gelatin capsule surrounding the end of a string is swallowed by the patient; the other end of the string is taped to their cheek. The capsule dissolves, and the string continues via peristalsis into the duodenum. After about 4 hours, the string is retrieved, and the mucous at the end of it is examined for parasites. Either a direct wet mount or a permanent stained smear can be made. This technique is ideal for finding Giardia sp. and some coccidian parasites.
An example of a parasite that can be retrieved by this method is shown in the image to the right, which shows a wet mount of an immature oocyst of coccidian parasite known as Cystoisospora belli (Isospora belli).
4. Centers of Disease Control and Prevention. "Cystoisosporiasis - Figure B: Immature oocyst of C. belli in an unstained wet mount showing two sporoblasts." CDC.gov, 16 Aug 2021, https://www.cdc.gov/dpdx/cystoisosporiasis/
