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Lab Test - Small Intestine Bacterial Overgrowth Breath Test

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Updated January 12, 2005

About the test: Although there are normally lots of bacteria in the large intestine, the small intestine is normally contains far less bacteria because stomach acid prevents bacteria from growing and because food is rapidly moved through it. However, certain conditions can allow bacteria to grow in the small intestine, including low stomach acid, parasite infection, intestinal scar tissue, diabetes, Crohn's disease and slow transit of food through the intestine. Health conditions it's used to assess: Digestive disorders with abdominal bloating and gas and possible diarrhea within one hour of eating. People with bacterial overgrowth may experience problems digesting dairy products or other carbohydrates. Unexplained weight loss, steatorrhea (fatty diarrhea) and Vitamin B12 deficiency are other clues to bacterial overgrowth.

What's involved: To perform the test, the patient takes a drink containing the sugar lactulose. If there is bacteria overgrowth in the small intestine, lactulose will ferment, producing the gases hydrogen and methane. Some of the gas is reabsorbed into the bloodstream and brought to the lungs. The breath test involves blowing into a mouthpiece, which collects the breath into vacuum-sealed collection tubes. It looks for increased hydrogen and methane in the exhaled breath. The more of these gases present, the greater the degree of bacterial overgrowth.
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