What is a Hydrogen Breath Test?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 03 October 2019
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A hydrogen breath test is a diagnostic test which is performed to learn more about the causes of gastrointestinal problems. This test is classically performed when it is suspected that someone is lactose intolerant or unable to process other sugars such as fructose. It may also be used to diagnose bacterial overgrowth in the small bowel or to test to see if food is moving through the intestinal tract too quickly, leading to malabsorption of food and nutrients. The test takes around two hours in most cases, with the patient going to a hospital or a clinic for the test.

The science behind the hydrogen breath test involves the bacteria which live in the bowel. Their waste products and concentrations change depending on the health of the host. In many people, if the bacteria are exposed to large amounts of undigested food, they begin to produce hydrogen, which is expressed in the breath. Overproduction of methane may also occur in association with or instead of hydrogen gas.


For a hydrogen breath test, the patient fasts for eight to 12 hours and then blows air into a balloon as a reference sample. Then, the patient is asked to drink a solution which can contain lactose, fructose, sorbitol, sucrose, lactulose, or another sugar. For the next two hours, periodic samples of the patient's breath are taken and tested for hydrogen, and sometimes methane. If hydrogen and/or methane levels are unusually high, it indicates that the patient has a problem along the digestive tract. A negative result does not necessarily mean the patient is clear, however, as some people do not have the hydrogen-producing bacteria which are manipulated for the test.

The hydrogen breath test is noninvasive and not painful, and is often scheduled for the morning so that patients can simply fast overnight to avoid undue hardship with the fasting requirement. Test results come back quickly, and a patient can discuss the implications of the result with the doctor. It is important that the patient not have taken antibiotics or anything else which would change the demographics of the bacteria in the gut for at least two weeks before the test, as this can skew the results.

Signs that may lead a doctor to recommend a hydrogen breath test include abdominal bloating, nausea, diarrhea, vomiting, gastrointestinal discomfort, and other signs that someone is not absorbing nutrients well or is having trouble processing food. By determining what is causing the problem, the doctor can make recommendations for treatment such as adjusting the patient's diet or prescribing antibiotics to bring the bacterial population back into balance.


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Post 3

I frequently experience indigestion and as a result I belch and expel gas a lot when in that state. Usually the breath that comes out as a result of the belching and gas expulsion smell very bad, and this is followed by long spell of diarrhea which subsides when I take antibiotics.

Do I need this hydrogen test?

Post 2

what has hydrogen test got to do with regular emptying of the bowels? if the result is negative what next?

Post 1

Where does someone go to get this test? Will every gastroenterologist offer this test? I have always had digestive problems quite frequently.

Also, I wonder if what I consume digests too quickly, especially pills which often seem to go straight through me.

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