Hydrogen Breath Test
William C. Shiel Jr., MD, FACP, FACR
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
- 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?
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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.
When is hydrogen breath testing used?
Hydrogen breath testing is used in the diagnosis of three conditions.
- The first is a condition in which dietary sugars are not digested normally. The most common sugar that is poorly digested is lactose, the sugar in milk. Individuals who are unable to properly digest lactose are referred to as lactose intolerant. Testing also may be used to diagnose problems with the digestion of other sugars such as sucrose, fructose and sorbitol.
- The second condition for which hydrogen breath testing is used is for diagnosing bacterial overgrowth of the small bowel, a condition in which larger-than-normal numbers of colonic bacteria are present in the small intestine.
- The third condition for which hydrogen breath testing is used is for diagnosing rapid passage of food through the small intestine. All three of these conditions may cause abdominal pain, abdominal bloating and distention, flatulence (passing gas in large amounts), and diarrhea.
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