String test

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Ascaris lumbricoides egg

Gelatin capsule in stomach

A string test involves swallowing a string to obtain a sample, which is then tested to detect the presence of intestinal parasites. The string test is rarely performed in the U.S.

Duodenal parasites test

You swallow a string with a weighted gelatin capsule on the end and then it is pulled back out after 4 hours. Any bile, blood, or mucus attached to the string is examined under the microscope for cell types and parts of parasites or eggs.

Food and fluid may be restricted for 12 hours before the test.

You may find it difficult to swallow the string, and you may feel an urge to vomit when the string is pulled up.

The test is performed when there is a suspicion of parasitic infestation but parasites are not detected by stool examination.

Review Date: 01/22/2007
Reviewed By: Jenifer K. Lehrer, MD, Department of Gastroenterology, Frankford-Torresdale Hospital, Jefferson Health System, Philadelphia, PA. Review provided by VeriMed Healthcare Network.