How does it work?

The hydrogen breath test measures the amount of hydrogen in a person’s breath. Very little hydrogen is normally detectable.

However, undigested lactose (milk protein) or fructose (sugar) in the colon or small intestine is fermented by bacteria and produces various gases, including hydrogen. The hydrogen is absorbed from the intestines, carried through the bloodstream to the lungs, and exhaled.

For a minority of people (less than 2% of the community) who do not produce breath hydrogen or methane, breath tests do not provide useful information.

What does it test for?

Hydrogen breath tests are commonly performed in people with irritable bowel syndrome (IBS) to rule out other underlying conditions.

Depending on how the test is performed, a hydrogen breath test can be used to test for food intolerances such as lactose intolerance, or intolerance to poorly absorbable sugars.

It can also be used to detect small intestine bacterial overgrowth (SIBO) which produces hydrogen in response to lactulose.

What does the test involve?

In this test, the person drinks a beverage containing fructose, lactose, or lactulose, and then they are asked to breathe out into a bag so that the breath is analyzed at regular intervals. Raised levels of hydrogen in the breath indicate improper digestion.

How should I prepare?

Your doctor will provide instructions on how long you may need to fast before the test. Certain foods, medications, and cigarettes can affect the accuracy of the test and should be avoided before taking the test. People should check with their doctor to make sure they are not taking medications that may interfere with test results.

Working with Your Doctor

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Successful relationships with healthcare providers are an important part of managing life with a long-term digestive disorder.

Doctor–Patient Communication

How to Help Your Doctor Help You

How to Talk to Your Doctor