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. It is rarely used today. It has been largely replaced by stool antigen and polymerase chain reaction (PCR) testing for Giardia.
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 abnormal cells, parasites, and 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 are 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 medicines can affect the test results.
Other string tests may be used for different conditions.
Alternative Names
Duodenal parasites test; Giardia - string test
References
Axelrad JE, Melia JMP. Infectious enteritis and proctocolitis. In: Chung RT, Rubin DT, Wilcox CM, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 12th ed. Philadelphia, PA: Elsevier; 2026:chap 112.
Fleckenstein JM. Approach to the patient with suspected enteric infection. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 262.
Hill DR. Giardiasis. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 322.
Mathison BA, Pritt BS. Medical parasitology. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 65.
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.
Review Date 4/27/2026
Updated by: Todd Eisner, MD, Private practice specializing in Gastroenterology in Boca Raton and Delray Beach, Florida at Gastroenterology Consultants of Boca Raton. Affiliate Assistant Professor, Florida Atlantic University School of Medicine. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.