A string test, also called the "Entero-test," is one type of test that may be used to detect the presence of parasites in the upper part of the small intestine. Intestinal parasites are microscopic organisms called "protozoa" and "helminths" that infect the intestines. Once established, they can go on to grow and thrive at the expense of the human host.
An abnormal test result may mean that you have giardia or another parasite in your system, which can cause nausea, vomiting, diarrhea, and other gastrointestinal problems.
Protozoa are one-celled organisms such as giardia that can cause chronic diarrhea and nutritional disorders, as well as fatigue, dizziness, joint pain, and hives. Common types of protozoa parasites include those that cause the following conditions:
- Amoebiasis: This condition is caused by the parasite Entamoeba histolytica. Symptoms include diarrhea, stomach cramps, and fever. It is most common in areas of poor sanitation, and may cause symptoms in travelers to developing countries. (Department of Health, Victoria, Australia)
- Giardiasis: This condition is caused by the parasite Giardia intestinalis, which is the most common parasite in the developed world.
- Cryptosporidiosis: This condition is caused by the parasite Cryptosporidium. This parasite is becoming prevalent in both developed countries and developing countries in patients with weakened immune systems, such as transplant recipients and those with AIDS, or in young children less than 5 years old.
Intestinal parasites are spread when tiny bits of fecal matter get into the mouth. This may be caused by contaminated food or water, through diaper changing, or during oral or anal sex. Other methods of spreading parasites include:
- swallowing 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
- traveling to foreign countries where parasites are more common
Helminths include flatworms, tapeworms, and roundworms that attach themselves to the lining of the small intestine and cause bleeding and nutrient loss. These types of parasites are most common in Africa, Asia, and Latin America, and tend to thrive in regions of the developing world that lack adequate water and sanitation facilities. (Michael O. Harhay, 2010) (Haque, 2007)
If you are experiencing an upset stomach, including diarrhea or vomiting, and you’ve been camping, traveling abroad, or doing other activities that may have put you at risk, your doctor may schedule a string test to rule out intestinal parasites. In the United States, stool samples are usually taken first, so you may be required to gather one or more samples at home that will then be examined for parasites in the lab. (Tulane University)
If the stool sample tests come back negative but you still have symptoms of a parasitic infection, the doctor may order a string test. The test is most often ordered when physicians suspect giardiasis or other upper intestinal parasites. (A.J. Bussalleu, 1985)
The string test, or Entero-test, is used to retrieve samples of the materials in the first part of the small intestine, just past the stomach. These samples are then examined under a microscope for the potential presence of parasites.
Prior to the test, you may be asked not to eat or drink anything for up to 12 hours. For the actual test, you’ll be swallowing 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 either to your cheek or the back of your neck just before you swallow the capsule.
You then take the capsule with water, just like you would take any pill. Once the pill is down, your doctor will likely advise you to sit back and relax for about four hours. (Children will 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. It will then be placed in a secure container and transported to the lab and examined within one hour.
The string test is very safe, and complications are rare. It may be a bit uncomfortable in some ways, however. For example, because the capsule has a string attached to it, it may feel strange or you may have trouble swallowing it.
In addition, when the string is pulled back up, you may feel the "gag" reflex and 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 fairly quickly, which means that the strange feelings 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 presence of intestinal parasites, and will most likely show which parasite you are infected with, 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.