Skip to main content
Explore URMC


Hydrogen Breath Testing

What is the hydrogen breath test?

The hydrogen breath test measures hydrogen gas in the breath and is used to diagnose several conditions that cause gastrointestinal symptoms. In humans, bacteria - specifically anaerobic bacteria in the colon - are capable of producing hydrogen. When bacteria is exposed to undigested sugars and carbohydrates, the bacteria produces hydrogen.  Typically there is a limited amount of undigested sugars that reach the colon, but in certain conditions a lack of digestion leads to a large number of undigested carbohydrate in the colon and increased amounts of hydrogen gas may be produced.

Increased amounts of hydrogen gas also may be produced when the colon bacteria move back into the small intestine, a condition called small intestinal bacterial overgrowth or SIBO (alternatively small bowel bacterial overgrowth or SBBO). In this instance, the bacteria are exposed to unabsorbed food that has not yet had a chance to completely traverse the small intestine to be fully digested and absorbed.

Some of the hydrogen gas that is produced in the intestine is then absorbed into the blood via the walls of the intestines.  It travels to the lung where it is released, exhaled in the breath, then measured.

When is hydrogen breath testing used?

Hydrogen breath testing is used in the diagnosis of three conditions.  Since these different conditions may require different substrates for testing, a single breath test may not be able to diagnose all of these conditions.

  1. Abnormal Digestion of Dietary Sugars:  Dietary sugars are not digested normally. The most common sugar that is poorly digested is lactose, the sugar in milk. Individuals who are unable to properly digest lactose are referred to as lactose intolerant. Testing also may be used to diagnose problems with the digestion of other sugars such as sucrose, fructose and sorbitol.
  2. Small Intestinal Bacterial Overgrowth (SIBO):  a condition in which larger-than-normal numbers of colonic bacteria are present in the small intestine.  Glucose is typically used as the substrate in this case, but sometimes the diagnosis can be suggested using one of the above substrates.
  3. Rapid Small Bowel Transit Time: food moves rapidly through the small intestine, which may cause abdominal pain, abdominal bloating and distention, flatulence (passing gas in large amounts), and diarrhea.

How do I get ready for this test?

  • For four (4) weeks before your test, you should not take any antibiotics by mouth. If on Erythromycin for Gastroporesis. You may continue this. Please call if you have questions regarding other antibiotics.
  • For one (1) week before your test, do not take any laxatives or stool softeners (for example Colace, Milk of Magnesia, Ex-Lax, Miralax) or fiber supplements (for example Metamucil or Citrucel). You should also not undergo any test that requires cleansing of the bowel, such as colonoscopy or barium enema one week before the test.
  • The day before your test:

You may consume only the following foods and drinks:  plain white bread, plain white rice, plain white potatoes, 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, milk, cheese, ice cream, yogurt and butter.

  • For 12 hours before your test:

You must stop eating and drinking 12 hours before the test.

For example, if your test is at 8:00 a.m., you would stop eating and drinking at 8:00 p.m. the night before.

You may continue to take your usual prescription medicines the night before the test. 

  • The day of your test:

You should not eat or drink anything in the morning. You may take your prescription 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. Oral hypoglycemic (diabetic) 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.


Your test may last for two to three hours. Please allow yourself sufficient time to complete your test.

You may wish to bring a book, magazine or office work to your appointment. Wireless internet is available. 

  • If you have questions regarding the test or your appointment, please call 275-4711.

The Test Procedure

  • The technician will verify that you have not had anything to eat or drink after 8 p.m. 
  • A breath sample will be collected by having you exhale into a bag.
  • A solution will be given to drink.  You should drink this whole amount. 
  • Breath samples will be collected every 20-30 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 to three 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.
  • Please contact the ordering provider to review the results in one week.

Related Topics