Hydrogen Breath Test

  • Medical Author:
    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    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.

woman with abdominal pain

How does hydrogen breath testing work?

The bacteria in the colon, including the anaerobic bacteria, are able to digest and use sugars and carbohydrates as food. When the anaerobic bacteria digest sugars and carbohydrates, they convert some of the sugars and carbohydrates into gases, most commonly hydrogen. They also may produce and release into the colon other substances, for example, chemicals that cause the colon to secrete water and cause diarrhea.

As previously discussed, some of the hydrogen gas is absorbed by the colon into the blood and is eliminated in the breath where it can be measured. As long as little sugar or carbohydrate reaches the colon, the small amounts of gas and other substances that are produced do not cause a problem. When larger amounts of sugar or carbohydrate reach the colon because they are not digested and absorbed in the small intestine, larger amounts of gas and substances are formed in the colon.

For example, if an individual digests and absorbs the sugar in milk (lactose) normally, then none of the lactose that is given for the lactose hydrogen breath test reaches the colon, and no increase in the concentration of hydrogen in the breath is seen during the breath test. On the other hand, if the individual does not digest andabsorb the lactose completely, that is, he or she is lactose intolerant, the lactose travels through the small intestine and enters the colon where the bacteria digest it and produce hydrogen. An increase in hydrogen in the breath then is seen. Other sugars for which poor digestion can be diagnosed by breath testing include sucrose and fructose (found in corn syrup), and sorbitol (a sugar that is used as a low-calorie sweetener).

There are ways other than abnormal digestion of dietary sugars by which the bacteria can cause problems. Unlike in the colon, the number of hydrogen-producing, anaerobic bacteria in the small intestine is small. If, however, large numbers of hydrogen-producing bacteria move into the small intestine from the colon, a condition called bacterial overgrowth of the small bowel, the bacteria may digest the sugars and carbohydrates before the small bowel has had a chance to digest and absorb them and produce large amounts of hydrogen.

Finally, if individuals have abnormally rapid passage of food through the small intestine, there may not be enough time for the small intestine to digest and absorb sugars and carbohydrates. This results in the entry of larger amounts of sugar and carbohydrate into the colon where the bacteria can digest and convert them to gas.

To diagnose bacterial overgrowth and rapid transit through the small intestine, a sugar that is not digested and absorbed by man, such as lactulose, usually is used for the test. In the case of rapid passage through the small intestine, the sugar passes quickly through the small intestine and into the colon so that hydrogen is found in the breath very soon after ingestion of the sugar. In the case of bacterial overgrowth, production of hydrogen occurs twice during the test. Once as the sugar passes the bacteria in the small intestine and again when the sugar enters the colon.

Medically Reviewed by a Doctor on 5/21/2015

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