What Is a String Test?

A string test, also called an “entero-test,” is one type of test used to detect the presence of parasites in the upper part of the small intestine. Once established, these parasites can grow and thrive at your expense.

An abnormal test result may mean you have Giardia intestinalis or another parasite in your system. Parasites can cause the following symptoms:

  • nausea
  • vomiting
  • diarrhea
  • upset stomach
  • other gastrointestinal problems

Intestinal parasites are spread when tiny bits of fecal matter get into the mouth. They may be contracted in the following ways:

  • ingesting contaminated food or water, as in:
    • swallowing contaminated water from swimming pools, lakes, rivers, ponds, or streams
    • accidentally swallowing something that’s come into contact with the stool of a person or animal
    • eating uncooked contaminated food
    • touching surfaces that may be contaminated with stool from an infected person, such as toys, bathroom fixtures, changing tables, or diaper pails, and then touching your eyes or mouth, or using utensils to eat that you have touched.
    • traveling to foreign countries where parasites are more common
  • changing a diaper
  • during oral or anal sex


Protozoa are one-celled organisms, such as Giardia intestinalis, that can find their way into your intestines and result in the following conditions and symptoms:

  • chronic diarrhea
  • nutritional disorders
  • fatigue
  • dizziness
  • joint pain
  • hives

Common types of protozoa parasites can cause a number of conditions, including amoebiasis, giardiasis, and cryptosporidiosis.


This condition is caused by the parasite Entamoeba histolytica. Symptoms include:

  • diarrhea
  • stomach cramps
  • fever

Amoebiasis is most common in areas with poor sanitation. You may get it traveling in developing countries.


This condition is caused by the parasite Giardia intestinalis, the most common parasite in the developed world.


This condition is caused by the parasite Cryptosporidium. This parasite is becoming more prevalent, in both developed and developing countries, in people with weakened immune systems, such as:

  • transplant recipients
  • people with AIDS
  • young children less than 5 years old


Helminths are tiny parasitic worms that can attach themselves to the lining of the small intestine and cause bleeding and nutrient loss. They tend to thrive in regions of the developing world that lack adequate water and sanitation facilities.

Helminths include:

  • flatworms
  • tapeworms
  • roundworms

Parts of the world where helminths are most common include:

  • Africa
  • Asia
  • Latin America

If you’re experiencing an upset stomach, including diarrhea or vomiting, and you’ve also been camping, traveling abroad, or engaging in other activities that put you at risk for contracting intestinal parasites, your doctor may schedule tests to rule out parasites. In the United States, the first test is usually a stool sample. You may be required to gather one or more samples at home that will be examined for parasites in the lab.

If your stool sample tests come back negative and you still have symptoms of a parasitic infection, your doctor may order the string test. Physicians most often order a string test when they think you may have giardiasis or other upper intestinal parasites.

The string test, or entero-test, is used to retrieve samples of materials in the first part of your small intestine, just past the stomach. These samples are examined under a microscope for the potential presence of parasites.

Prior to the test, you may be asked to abstain from eating or drinking for up to 12 hours. For the actual test, you’ll swallow a gelatin capsule, much like a vitamin supplement. This capsule contains a spool of nylon string and a weight, to help it go down into your stomach. The end of the string is usually taped to your cheek or the back of your neck just before you swallow the capsule.

Once the pill is down, your doctor will likely advise you to sit back and relax for about four hours. Children often sleep during this part of the test. As you rest, your natural digestive processes will gradually dissolve and move the capsule down through your stomach, unraveling the spool of string as it goes. Meanwhile, the string gathers materials from the stomach and upper intestine, including any potential parasites.

After the specified amount of time, the string will be pulled back up out of your stomach through your throat, placed in a secure container, and transported to the lab for examination within one hour.

The string test is very safe and complications are rare. However, it may be a bit uncomfortable because the capsule has a string attached to it. It may feel strange to you, or you may have trouble swallowing the capsule.

In addition, when the string is pulled back up, you may feel your “gag” reflex or feel like you want to vomit. However, the string is very small and thin and will not hurt you as it comes back up. The doctor will likely remove the string quickly, meaning these strange sensations won’t last long. On rare occasions, a mild superficial lesion caused by the string retrieval may result in some bleeding.

A positive test will reveal the type and presence of intestinal parasites, helping doctors determine the type of treatment that is best for you. If the test comes back showing no abnormalities, your stomach discomfort and other symptoms are not likely to be caused by intestinal parasites.