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Hydrogen Breath Test Procedure

The hydrogen breath test is a test that uses the measurement of hydrogen in the breath to diagnose several conditions that cause gastrointestinal symptoms. In humans, only bacteria - specifically, anaerobic bacteria in the colon - are capable of producing hydrogen. The bacteria produce hydrogen when they are exposed to unabsorbed food, particularly sugars and carbohydrates, not proteins or fats. Although limited hydrogen is produced from the small amounts of unabsorbed food that normally reach the colon, large amounts of hydrogen may be produced when there is a problem with the digestion or absorption of food in the small intestine, that allows more unabsorbed food to reach the colon.

Large amounts of hydrogen also may be produced when the colon bacteria move back into the small intestine, a condition called bacterial overgrowth of the small bowel. In this latter instance, the bacteria are exposed to unabsorbed food that has not had a chance to completely traverse the small intestine to be fully digested and absorbed. Some of the hydrogen produced by the bacteria, whether in the small intestine or the colon, is absorbed into the blood flowing through the wall of the small intestine and colon. The hydrogen-containing blood travels to the lungs where the hydrogen is released and exhaled in the breath where it can be measured.

Preparation for the Test


For six (2) weeks before your test:

  • You should not take any antibiotics.

The day before your test:

  • You may consume only the following foods and drinks: plain white bread, plain white rice, baked or broiled chicken or fish, water, non-flavored black coffee or tea.
  • Only salt may be used to flavor your food.
  • Butter or margarine is not permitted.
  • Soda Pop/cola drinks are not permitted.
  • DO NOT EAT OR DRINK ANYTHING ELSE – it could give false results for the test. Specifically, avoid beans, pasta, fiber cereals, high fiber foods, fruits and vegetables, and baked white potatoes.
  • The night before the test, have an early dinner of rice and meat.

For 12 hours before your test:

  • You must stop eating and drinking 12 hours before the test. For example, if your test is at 9:00 a.m., you would stop eating and drinking at 9:00 pm the night before.
  • Take no medications the morning of your test.
  • Please bring all prescription medications to your appointment.

The day of your test:

  • You should not eat or drink anything in the morning. You may take your medications with a small amount of water.
  • If you are diabetic requiring insulin or diabetic pills, ask your physician if you should change your morning dose. Generally, half of your normal long acting insulin is given the night before.
  • Oral hypoglycemic medications are usually not taken that morning until completion of the test and resumption of eating meals.
  • Two hours before the test, brush your teeth.
  • DO NOT EAT, DRINK, CHEW GUM OR TOBACCO, SMOKE CIGARETTES, EAT BREATH MINTS OR CANDY BEFORE OR DURING THE TEST.
  • Do not sleep or exercise while the test is being done.

Your test may last for two to four hours. Please allow yourself sufficient time to complete you test.

The Test Procedure

  • The technician will verify that you have not had anything to eat or drink after midnight
  • A breath sample will be collected by having you exhale into bag.
  • A solution of lactose, lactulose, or fructose will be given to drink. You should drink this whole amount.
  • Breath samples will be collected every 15 minutes. After each sample is collected, the sample will be removed from the bag with a syringe, allowing collection of another sample into the bag.
  • During the test, you should take notice of your symptoms and inform the technician if you have your typical symptoms for which the test is being performed.
  • During the test, you should not eat, chew candy, smoke, sleep, or exercise.
  • When the test is over, generally after two or four hours, you may leave. You may return to your usual diet and activity after the test.
  • The samples will be processed in the afternoon. The report will be sent to your doctor.

Principles of Hydrogen Breath Testing

  • Hydrogen gas in the body is produced from intestinal bacteria. Bacteria, normally in the large intestine, produce hydrogen through fermentation of carbohydrates – such as lactose, lactulose, and fructose which are substrates given for the hydrogen breath test. Some of the hydrogen produced by bacteria is absorbed by intestinal mucosa whereby it enters the vasculature and is transported to the lungs.
  • Hydrogen is then exhaled by the lungs by normal breathing. This is collected in the bag for subsequent analysis.
  • In small intestinal bacterial overgrowth, the small intestinal bacteria metabolize the lactulose given and produce an early rise in the breath hydrogen.
  • In lactose intolerance, the individual has a deficiency in lactase, the enzyme that breaks down lactose. Normally, lactose is broken down in the small intestine by lactase and very little lactose reaches the large intestine where the bacteria break it down to produce hydrogen. In lactose intolerance (lactase deficiency), the ingested lactose is not metabolized in the small intestine and reaches the colon where it is metabolized by colonic bacteria producing a large amount of hydrogen which is measured in the breath sample.