Duodenal parasites test

Alternative names
String test

The string test involves swallowing a string to obtain a sample, which is then tested to detect the presence of intestinal parasites.

How the test is performed
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 segments of parasites or eggs.

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

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child’s age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child’s age:

  • Infant test or procedure preparation (birth to 1 year)  
  • Toddler test or procedure preparation (1 to 3 years)  
  • Preschooler test or procedure preparation (3 to 6 years)  
  • Schoolage test or procedure preparation (6 to 12 years)  
  • Adolescent test or procedure preparation (12 to 18 years)

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

Why the test is performed

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

Normal Values
No presence of blood, parasites, fungus, abnormal cells, or bile is normal.

What abnormal results mean
Abnormal results may indicate the presence of giardia or another parasitic infestation.

Special considerations
Previous drug therapy can affect the test results.

Johns Hopkins patient information

Last revised: December 3, 2012
by Martin A. Harms, M.D.

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