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.