Hydrogen breath test (HBT)

A test to establish whether you have a small bowel bacterial overgrowth or an intolerance to a specific sugar

What is a hydrogen breath test?

A hydrogen breath test provides information about the digestion of certain sugars or carbohydrates such as milk sugar (lactose) or fruit sugar (fructose). This helps to determine if you are intolerant to certain sugars.

The test also detects abnormal growth of bacteria in the small bowel.

Need to know

  • What happens during the HBT test? icon plus

    Your consultant will verify that you have not had anything to eat or drink apart from water for the previous 12 hours. A breath sample will be collected by having you exhale into the test machine. A glass of water mixed with either lactose, non-absorbable sugar laxative, or fructose will be given to you to drink. You should drink the whole amount. Breath samples will be collected approximately every 15 minutes.

    During the test, you should take note of your symptoms and inform your consultant if you have your typical symptoms for which the test is being performed. When the test is over, after between two and four hours, you may leave.
  • How to prepare icon plus

    For four weeks before your test you should not take any antibiotics. For one week before your test you should not take any laxatives, stool softeners or stool bulking agents.

    The day before your test you will have a restricted diet. Your consultant will tell you what you can and cannot eat. Apart from water, you must stop eating and drinking 12 hours before your test.

    Check with your consultant if you need to take regular medication during this time. Do not chew gum, smoke cigarettes, eat breath mints or other sweets before or during your test. Do not sleep or exercise while the test is being done. Your test may last for two to four hours.
  • After the test icon plus

    You will be allowed to go home after the test has finished. You do not need to take any special precautions and can eat and drink normally. There are no serious risks, however you may experience some symptoms during or after the tests.

    Some patients are sensitive to fermentation of sugars that are administered during tests or may have lactose intolerance. This can cause nausea, bloating and sometimes mild to moderate pain during or soon after the study. However, these symptoms are self-limiting and in the majority of patients settle within a few hours.

    If you have any concerns regarding symptoms contact your consultant or nurse specialist.

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This content is intended for general information only and does not replace the need for personal advice from a qualified health professional.
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