A hydrogen breath test is a clinical test used to diagnose people for common food intolerances and irritable bowel syndrome. This test is frequently used to diagnose lactose intolerance. The test is very simple and is completely non-invasive. During the test patients are tested for not only hydrogen but also methane. These gases are produced as a result of foods that remain in the intestines undigested. In the case of lactose intolerance people who do not produce enough lactase will be unable to digest lactose, this test will measure whether lactose is actually being digested or not.

If your doctor has suggested you have a hydrogen breath test there will be a few things you will need to do to prepare for this test. You may not have had a colonoscopy, barium enema, or any other test that requires a bowel prep to be done since this prep will cleanse the bacteria in the bowel. This bacteria must be present to do the hydrogen breath test, so you will need to wait 4 weeks after these procedures to have this test done.

During the 4 weeks prior to the tests you may also not have taken any antibiotics or Pepto Bismol. 24 hours prior to the test you should not smoke and the day of the test you should abstain from chewing gum, using mouthwash, or toothpaste and you will be asked to fast for 8 hours prior to the test as well.

In the case of lactose malabsorption testing basing readings of hydrogen levels are taken of the patient’s breath. The patient then drinks a liquid that is pure lactose, approximately 20 to 25 g. The patient’s breath is then measured every 15 to 30 minutes for about 3 hours.  Doctors are looking for levels of hydrogen that are 20ppm above the lowest preceding value at the beginning of the test. Levels above this mark will result in a diagnosis of lactose intolerance.

Methane levels are also measured, as some patients may produce exaggerated levels of methane rather than hydrogen and some patients may produce both gasses. With methane gasses any level that is 12 ppm higher than the original value is considered a positive diagnosis for lactose intolerance. For a patient that produces both gasses, the two values are added together and averaged, with 15 ppm being the number that most doctors are looking for, for this combined value.