Hydrogen Breath Test

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Medical Author: Jay W. Marks, M.D.
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR

• What is the hydrogen breath test?
• When is hydrogen breath testing used?
• How does hydrogen breath testing work?
• How is hydrogen breath testing performed?
• How are the results of hydrogen breath testing interpreted?
• What are the limitations of hydrogen breath testing?
• Are there other ways in which hydrogen breath testing can be used?
• What are the side effects of hydrogen breath testing?
• What are the alternatives to hydrogen breath testing?

What is the hydrogen breath test?

The hydrogen breath test is a test that uses the measurement of hydrogen in the breath to diagnose several conditions that cause gastrointestinal symptoms. In humans, only bacteria - specifically, anaerobic bacteria in the colon - are capable of producing hydrogen. The bacteria produce hydrogen when they are exposed to unabsorbed food, particularly sugars and carbohydrates, not proteins or fats. Although limited hydrogen is produced from the small amounts of unabsorbed food that normally reach the colon, large amounts of hydrogen may be produced when there is a problem with the digestion or absorption of food in the small intestine, that allows more unabsorbed food to reach the colon.

Large amounts of hydrogen also may be produced when the colon bacteria move back into the small intestine, a condition called bacterial overgrowth of the small bowel. In this latter instance, the bacteria are exposed to unabsorbed food that has not had a chance to completely traverse the small intestine to be fully digested and absorbed. Some of the hydrogen produced by the bacteria, whether in the small intestine or the colon, is absorbed into the blood flowing through the wall of the small intestine and colon. The hydrogen-containing blood travels to the lungs where the hydrogen is released and exhaled in the breath where it can be measured.

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