Hydrogen Breath Test

The hydrogen breath test is a test that uses the measurement of hydrogen in the breath to diagnose several conditions that cause gastrointestinal symptoms.

Hydrogen breath testing is used in the diagnosis of three conditions:

  1. Dietary sugars, such as lactose, sucrose, fructose and sorbitol, are not digested normally
  2. Bacterial overgrowth of the small bowel, a condition in which larger-than-normal numbers of colonic bacteria are present in the small intestine
  3. Rapid passage of food through the small intestine.

All three of these conditions may cause abdominal pain, cramps, abdominal bloating and distention, flatulence (passing gas in large amounts), and diarrhea.


  • No antibiotic for two weeks and/or no recent or current diarrhea.
  • Do not eat any of the following foods 24 hours prior to the test:
  • What you can eat before the test:
  • No smoking one hour prior to test
  • Check for allergies, especially citrus


Prior to hydrogen breath testing, you will fast for at least 12 hours and will be asked about your weight. At the start of the test, you will blow into and fill a balloon with a breath of air, collecting two baseline breath samples 15 minutes apart. The concentration of hydrogen is measured in a sample of breath removed from the balloon. You will then ingest a small amount of the test sugar (lactose, sucrose, sorbitol, fructose, lactulose, etc. depending on the purpose of the test). Additional samples of breath are collected and analyzed for hydrogen every 30 minutes for three and up to five hours. Staff will also record any symptoms you experience during the test.


Interpretation of the results depend on the sugar that is used for testing, and the pattern of hydrogen production after the sugar is ingested.

After ingestion of test doses of the dietary sugars lactose, sucrose, fructose or sorbitol, any production of hydrogen means that there has been a problem with digestion or absorption of the test sugar and that some of the sugar has reached the colon.

When rapid passage of food through the intestine is present, the test dose of lactulose reaches the colon more quickly than normally, and, therefore, hydrogen is produced by the colon’s bacteria soon after the sugar is ingested.

When bacterial overgrowth of the small bowel is present, ingestion of lactulose results in two separate periods during the test in which hydrogen is produced, an earlier period caused by the bacteria in the small intestine and a later one caused by the bacteria in the colon.

Side Effects

The side effects of hydrogen breath testing are exactly what one would expect to see in individuals who poorly digest and absorb sugars and carbohydrates, for example, bloating, distention, pain, and diarrhea. When lactulose is used these symptoms are unlikely to occur or are mild because the dose of lactulose used for testing is small.