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String test


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 is done if the stool sample is negative.

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 parasite infection such as giardia.


Treatment with certain drugs can affect the test results.


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Hill DR, Nash TE. Giardia lamblia. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, Updated Edition. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 281.

Siddiqi HA, Salwen MJ, Shaikh MF. Laboratory diagnosis of gastrointestinal and pancreatic disorders. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 23rd ed. Philadelphia, PA: Elsevier; 2017:chap 22.

Review Date: 4/11/2018
Reviewed By: Michael M. Phillips, MD, Clinical Professor of Medicine, The George Washington University School of Medicine, Washington, DC. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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