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String test

Definition

A string test involves swallowing a string to obtain a sample from the upper part of the small intestine. The sample is then tested to look for intestinal parasites.

Alternative Names

Duodenal parasites test; Giardia - string test

How the Test is Performed

To have this test, you swallow a string with a weighted gelatin capsule on the end. The string is pulled out 4 hours later. Any bile, blood, or mucus attached to the string is examined under the microscope. This is done to look for cells and parasites or parasite eggs.

How to Prepare for the Test

You may be asked not to eat or drink anything for 12 hours before the test.

How the Test will Feel

You may find it hard to swallow the string. You may have an urge to vomit when the string is being removed.

Why the Test is Performed

The test is performed when your health care provider suspects that you have a parasite infection. Usually a stool sample is tested first. A string test may be done if the stool sample is negative but a parasite infection is still suspected.

Normal Results

No blood, parasites, fungi, or abnormal cells is normal.

Normal value ranges may vary slightly among different laboratories. Talk to your provider about the meaning of your test results.

What Abnormal Results Mean

Abnormal results may be a sign of parasite infection, such as giardia.

Considerations

Treatment with certain drugs can affect the test results.

Gallery

Ascaris lumbricoides egg
This is an egg of Ascaris lumbricoides. Ascarides are roundworms, a common parasitic infection throughout the world. It is estimated that as many as 1 billion people (one sixth of the world population) may be infected with roundworms.
Ascaris lumbricoides egg
This is an egg of Ascaris lumbricoides. Ascarides are roundworms, a common parasitic infection throughout the world. It is estimated that as many as 1 billion people (one sixth of the world population) may be infected with roundworms.

References

Adam RD. Giardiasis. In: Ryan ET, Hill DR, Solomon T, Aronson NE, Endy TP, eds. Hunter's Tropical Medicine and Emerging Infectious Diseases. 10th ed. Philadelphia, PA: Elsevier; 2020:chap 95.

Melia JMP, Sears CL. Infectious enteritis and proctocolitis. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 110.

Siddiqi HA, Rabinowitz S, Axiotis CA.. Laboratory diagnosis of gastrointestinal and pancreatic disorders. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 23.

Wojewoda CM. Stempak LM. Medical bacteriology. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 57.

Last reviewed May 6, 2022 by Michael M. Phillips, MD, Emeritus Professor of Medicine, The George Washington University School of Medicine, Washington, DC. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team..

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