What to Know About the String Test

Medically Reviewed by Dan Brennan, MD on June 15, 2021
4 min read

The string test, which is also called the Entero-test, is a test used to find parasites in the upper part of your gastrointestinal tract. To perform the test, you swallow a string. When the string is pulled out, it's examined under a microscope to look for parasites.

You may need a string test if your doctor thinks you might have a parasite in your intestines. Normally, you will have a stool sample tested first. A string test may be done if your stool sample is negative. 

The string test consists of a weighted gelatin capsule with a string attached to it. You tape one end of the string to your cheek and then swallow the capsule. You leave the string in for 4 to 6 hours or overnight. You won't eat anything while the string is in place. The string is then removed. It will be examined under a microscope to check for signs of a parasite. 

Some parasites can live in your intestines for years without causing symptoms. If you do have symptoms, they may include: 

  • Diarrhea
  • Nausea
  • Vomiting
  • Bloating
  • Gas
  • Loose stools with blood and mucus
  • Stomach pain or tenderness
  • Weight loss
  • Tiredness
  • Worms in your stool
  • Rash or itching around your rectum 

Intestinal parasites are usually spread through fecal-to-oral transmission. This happens when you swallow a tiny bit of fecal matter. Some methods of fecal-to-oral transmission include: 

  • Eating raw fruits or vegetables washed in contaminated water
  • Eating raw shellfish that was grown in contaminated water
  • Drinking water contaminated with raw sewage
  • Swimming in pools that are contaminated
  • Swimming in lakes or ocean waters that are contaminated with raw sewage
  • Sexual activity involving mouth-to-anus contact

Intestinal parasites are more common in undeveloped parts of the world, but some are still prevalent in the United States, including: 

Enterobius vermicularis. This is also called pinworm. It's the most common intestinal parasite in the United States. This causes itching around the anus and vagina. It's especially prevalent in children. Over 30% of children in the world are infected. 

Giardia lamblia. This is the most common intestinal infection in the world and the second most common in the United States. Giardia survives well in cold mountain streams and frequently infects people who spend a lot of time outdoors. Its nickname is "backpacker's diarrhea". Symptoms usually appear 1 to 2 weeks after exposure.  

Ancylostoma duodenale and necator americanus. These are types of hookworms. Hookworms live in the small intestines. Most hookworm infestations don't cause symptoms. The most serious complication with hookworms is anemia from blood loss.

Entamoeba histolytica. This parasite causes a disease called amebiasis. It usually happens in areas where living conditions are crowded and unsanitary. It's rare in the United States but sometimes occurs in people who have recently traveled to or immigrated from areas where it's common such as parts of Africa, Latin America, and Asia. It can spread quickly to many people through contaminated water.

Some factors that can increase your risk of getting intestinal parasites include: 

  • Having HIV/AIDS
  • A weakened immune system
  • Traveling internationally
  • Visiting or living in an area with parasites
  • Being old or young
  • Poor hygiene
  • Unsanitary food and water
  • Being in institutional care
  • Being in child care centers

The treatment for your parasitic infection will depend on what's causing it. Some parasitic infections don't need treatment and will go away on their own. Some antiparasitic medicines get rid of the parasite. In the case of some worm parasites, the medicine reduces the number of worms so that the symptoms clear up. Some antibiotics and antifungal medicines can treat other kinds of parasites. 

You can reduce your risk of getting intestinal parasites with the following guidelines: 

  • Avoid drinking untreated lake or stream water.
  • Avoid swallowing pool water or water in water parks.
  • Make sure your food is adequately cooked.
  • Make sure your water isn't contaminated. 
  • Avoid drinking tap water when you're traveling to areas with parasites. 
  • Follow the "Cook it, boil it, peel it, or forget it" rule for food when traveling to areas with parasites. 

Wash your hands in the following situations: 

  • Before you eat
  • After you use the toilet
  • Before, during, and after you prepare food
  • Before and after you take care of someone who is sick
  • Before and after you treat a cut or wound
  • After you touch an animal or animal waste
  • After you change a child's diaper or help a child use the toilet