Stool Tests

Stool Tests

Lea este articulo

About Stool Tests

Stool (or feces) is usually thought of as nothing but waste — something to quickly flush away. But bowel movements can provide doctors with valuable information as to what's wrong when a child has a problem in the stomach, intestines, or another part of the gastrointestinal system.

A doctor may order a stool collection to test for a variety of possible conditions, including:

  • allergy or inflammation in the body, such as part of the evaluation of milk protein allergy in infants
  • infection, as caused by some types of bacteria, viruses, or parasites that invade the gastrointestinal system
  • digestive problems, such as the malabsorption of certain sugars, fats, or nutrients
  • bleeding inside of the gastrointestinal tract

The most common reason to test stool is to determine whether a type of bacteria or parasite may be infecting the intestines. Many microscopic organisms living in the intestines are necessary for normal digestion. If the intestines become infected with harmful bacteria or parasites, though, it can cause problems like certain types of bloody diarrhea, and testing stool can help find the cause.

Stool samples are also sometimes analyzed for what they contain; for instance, examining the fat content. Normally, fat is completely absorbed from the intestine, and the stool contains virtually no fat. In certain types of digestive disorders, however, fat is incompletely absorbed and remains in the stool.

Collecting a Stool Specimen

Unlike most other lab tests, stool is sometimes collected by the child's family at home, not by a health care professional. Here are some tips for collecting a stool specimen:

  • Collecting stool can be messy, so be sure to wear latex gloves and wash your hands and your child's hands well afterward.
  • Many kids with diarrhea, especially young children, can't always let a parent know in advance when a bowel movement is coming. Sometimes a hat-shaped plastic lid is used to collect the stool specimen. This catching device can be quickly placed over the toilet bowl or your child's rear end to collect the specimen. Using a catching device can prevent contamination of the stool by water and dirt. If urine contaminates the stool sample, it will be necessary to take another sample. Also, if you're unable to catch the stool sample before it touches the inside of the toilet, the sample will need to be repeated. Fishing a bowel movement out of the toilet does not provide a clean specimen for the laboratory to analyze.
  • Another way to collect a stool sample is to loosely place plastic wrap across the rim of the toilet, under the seat. Then place the stool sample in a clean, sealable container before taking to the laboratory. Plastic wrap can also be used to line the diaper of an infant or toddler who is not yet using the toilet.

The stool should be collected into clean, dry plastic jars with screw-cap lids. You can get these from your doctor or through hospital laboratories or pharmacies, although any clean, sealable container could do the job. For best results, the stool should then be brought to the laboratory immediately.

If the stool specimen is going to be examined for an infection, and it's impossible to get the sample to the laboratory right away, the stool should be refrigerated, then taken to the laboratory to be cultured as soon as possible after collection. When the sample arrives at the lab, it is either examined and cultured immediately or placed in a special liquid medium that attempts to preserve potential bacteria or parasites.

The doctor or the hospital laboratory will usually provide written instructions on how to successfully collect a stool sample; if written instructions are not provided, take notes on how to collect the sample and what to do once you've collected it.

If you have any questions about how to collect the specimen, be sure to ask. The doctor or the lab will also let you know if a fresh stool sample is needed for a particular test, and if it will need to be brought to the laboratory right away.

Most of the time, disease-causing bacteria or parasites can be identified from a single stool specimen. Sometimes, however, up to three samples from different bowel movements must be taken. The doctor will let you know if this is the case.

Testing the Stool Sample

In general, the results of stool tests are usually reported back within 3 to 4 days, although it often takes longer for parasite testing to be completed.

Examining the Stool for Blood

Your doctor will sometimes check the stool for blood, which can be caused by certain kinds of infectious diarrhea, bleeding within the gastrointestinal tract, and other conditions. However, most of the time, blood streaking in the stool of an infant or toddler is from a slight rectal tear, called a fissure, which is caused by straining against a hard stool (this is fairly common in infants and kids with ongoing constipation).

Testing for blood in the stool is often performed with a quick test in the office that can provide the results immediately. First, stool is smeared on a card, then a few drops of a developing solution are placed on the card. An instant color change shows that blood is present in the stool. Sometimes, stool is sent to a laboratory to test for blood, and the result will be reported within hours.

Culturing the Stool

Stool can be cultured for disease-causing bacteria. A stool sample is placed in an incubator for at least 48 to 72 hours and any disease-causing bacteria are identified and isolated. Remember that not all bacteria in the stool cause problems; in fact, about half of stool is bacteria, most of which live there normally and are necessary for digestion. In a stool culture, lab technicians are most concerned with identifying bacteria that cause disease.

For a stool culture, the lab will need a fresh or refrigerated sample of stool. The best samples are of loose, fresh stool; well-formed stool is rarely positive for disease-causing bacteria. Sometimes, more than one stool will be collected for a culture.

Swabs from a child's rectum also can be tested for viruses. Although this is not done routinely, it can sometimes give clues about certain illnesses, especially in newborns or very ill children. Viral cultures can take a week or longer to grow, depending on the virus.

Testing the Stool for Ova and Parasites

Stool may be tested for the presence of parasites and ova (the egg stage of a parasite) if a child has prolonged diarrhea or other intestinal symptoms. Sometimes, the doctor will collect two or more samples of stool to successfully identify parasites. If parasites — or their eggs — are seen when a smear of stool is examined under the microscope, the child will be treated for a parasitic infestation. The doctor may give you special collection containers that contain chemical preservatives for parasites.

Reviewed by: Steven Dowshen, MD
Date reviewed: September 2011

Related Articles
Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.
© 1995-2014 The Nemours Foundation/KidsHealth. All rights reserved.