Health Guide

Hydrogen breath test

What is this test?

This test measures the level of hydrogen gas in air that is exhaled (breathed out). This test is done after drinking a fixed amount of sugar. It is used to evaluate and manage certain intestinal disorders[1] such as lactose intolerance[2][1][3][4].

What are other names for this test?

  • H2BT - Hydrogen breath test
  • H-BT - Hydrogen breath test

Why do I need this test?

Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. You may need this test if you have:

  • Bacterial overgrowth syndrome
  • Lactose intolerance

When and how often should I have this test?

When and how often laboratory tests are done may depend on many factors. The timing of laboratory tests may rely on the results or completion of other tests, procedures, or treatments. Lab tests may be performed immediately in an emergency, or tests may be delayed as a condition is treated or monitored. A test may be suggested or become necessary when certain signs or symptoms appear.

Due to changes in the way your body naturally functions through the course of a day, lab tests may need to be performed at a certain time of day. If you have prepared for a test by changing your food or fluid intake, lab tests may be timed in accordance with those changes. Timing of tests may be based on increased and decreased levels of medications, drugs or other substances in the body.

The age or gender of the person being tested may affect when and how often a lab test is required. Chronic or progressive conditions may need ongoing monitoring through the use of lab tests. Conditions that worsen and improve may also need frequent monitoring. Certain tests may be repeated to obtain a series of results, or tests may need to be repeated to confirm or disprove results. Timing and frequency of lab tests may vary if they are performed for professional or legal reasons.

How should I get ready for the test?

Eat a low fiber diet the day before the test[4].

How is the test done?

You will be asked to drink a liquid that contains sugar[5]. Breath samples will be collected in a balloon or bag, and hydrogen levels are measured using special techniques[6].

How will the test feel?

The amount of discomfort you feel will depend on many factors, including your sensitivity to pain. Communicate how you are feeling with the person doing the test. Inform the person doing the test if you feel that you cannot continue with the test.

What should I do after the test?

There are no special instructions to follow after this test.

What are the risks?

Ask the healthcare worker to explain the risks of this test or procedure to you before it is performed.

What are normal results for this test?

Laboratory test results may vary depending on your age, gender, health history, the method used for the test, and many other factors. If your results are different from the results suggested below, this may not mean that you have a disease. Contact your healthcare worker if you have any questions. The following are considered to be normal results for this test:

  • Adults (bacterial overgrowth): Increase of <12 ppm to 20 ppm from baseline[6]
  • Adults (lactose intolerant): Increase of <20 ppm above baseline [1][4]

What might affect my test results?

  • Methane producers [4]

What follow up should I do after this test?

Ask your healthcare worker how you will be informed of the test results. You may be asked to call for results, schedule an appointment to discuss results, or notified of results by mail. Follow up care varies depending on many factors related to your test. Sometimes there is no follow up after you have been notified of test results. At other times follow up may be suggested or necessary. Some examples of follow up care include changes to medication or treatment plans, referral to a specialist, more or less frequent monitoring, and additional tests or procedures. Talk with your healthcare worker about any concerns or questions you have regarding follow up care or instructions.

Where can I get more information?

Related Companies

  • National Digestive Diseases Information Clearinghouse (NDDIC) -
  • American Academy of Pediatrics -


[1] Swagerty DL Jr, Walling AD, & Klein RM: Lactose intolerance. Am Fam Physician 2002; 65(9):1845-1850.

[2] The American Gastroenterological Association: What diagnostic tests are used to detect lactose intolerance. American Gastroenterological Association. Bethesa, MD, USAAvailable from URL: http;// As accessed May 9, 2005.

[3] Shaw AD & Davies GJ: Lactose intolerance problems in diagnosis and treatment.. J Clin Gastroenterol. 1999; 28:208-16.

[4] Arola H: Diagnosis of hypolactasia and lactose malabsorption. Scand J Gastroenterol 1994; 29(Suppl 202):26-35.

[5] National Digestive Diseases Information Clearinghouse: Lactose Intolerance. 03-2751. National Institutes of Health. Bethesda, MD, USA. 2003. Available from URL: As accessed May 12, 2005.

[6] Fine KD & Schiller LR: AGA technical review on the evaluation and management of chronic diarrhea. Gastroenterology 1999; 116/6:1464-86.

Last Updated: 7/4/2018
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