Physicians often rely on a child’s or the parent’s report of symptoms when diagnosing and determining the treatment for diarrhea. A medical history will include questions about the duration and severity of symptoms, eating habits and current medications. A physical examination will allow a physician to look for signs of illness that may be causing the diarrhea.

Most children with diarrhea will not need extensive testing. When diarrhea goes away by itself, it is usually not necessary to submit to various tests to determine the cause of diarrhea. When tests are used, they may include:

• Stool tests. Stool (feces) is tested for bacteria, parasites or other signs of infection that may be causing the diarrhea.
  
  
• Blood tests. Blood is drawn and tested for evidence of disease (e.g., bacterial infection) that may be causing the diarrhea.
  
  
• Fasting tests. Under the guidance of a physician the child is asked to avoid certain products to determine whether an allergy or food intolerance may be responsible for the diarrhea. Bowel habits are observed to identify whether a change in diet affects the diarrhea. Physicians commonly ask children to avoid dairy products, carbohydrates and wheat, although other foods may be included. Milk may be purchased with added lactase, and yogurt is usually well-tolerated.
  
  
• Endoscopy. A flexible tube (with attached light and camera) is inserted into a child’s digestive tract to identify any abnormalities that may be causing the diarrhea. Biopsies (tissue samples) and color photographs may be taken during this procedure. In a colonoscopy, the tube is inserted via the anus and usually through the entire colon. A sigmoidoscopy is similar, but only goes as far as the lower part of the colon (the sigmoid colon).