the hydrogen breath test

proper diagnosis of food intolerances

The most common means of diagnosis is a hydrogen breath test. All other test methods like IgG-Blood test, biofeedback or any other method are not valid and there's no scientific background or evidence at all. A proper diagnosis cannot be done at home!

H2 breath test

h2_testThe patient drinks a certain amount of a sugar solution on an empty stomach. Afterwards the patient will be asked to blow several times, at certain intervals (normally every half hour or every 10 minutes), into a device that measures the hydrogen (H2) levels from the air exhaled.

Since the sugar is not being properly digested there are bacteria in the intestines which produce hydrogen, short-chained fatty acids and CO2. The hydrogen reaches the bloodstream via the large intestine and will consequently be exhaled through the lungs. By measuring the levels of hydrogen (which, by the way, does not itself cause any symptoms) it is possible to perform a diagnosis using this non-invasive breath test.

Preparing for the test

Your doctor should provide you with detailed information ahead of the test in order to be able to obtain a diagnostically conclusive result.

This includes:

  • your needing to observe a short fasting period (12 hours before, no eating, just drink water)
  • not using any toothpaste  this seems to be obsolete - you may brush your teeth, but don't use mouthwash!
  • not smoking on the day of the test - smokers have high levels of CO in their breath which triggers the H2-sensor!
  • you should not have had a colonoscopy or an enteroscopy or have taken any antibiotics in the last four weeks before the test is administered
  • Do not work out before the test

The test

You'll get a certain amount of a test solution (water + to be tested sugar) to drink. Then you will be asked to blow into a measuring device, which measures the hydrogen content of your breathing air, at defined intervals.
The values ​​of this measurement are expressed in ppm (parts per million). The first value, which is measured before the solution is drunk, is the initial value (basal value). The following values, along with the symptoms that occur, are listed in a table. If one of the values ​​(or two successive values) exceeds 20 ppm above the basal value, the test is positive. Exception: The test for SIBOS with lactulose (see below). After 2-3 hours, the test is usually over, but the test may need to be extended to up to 4 hours.

Apart from measuring the H2 values, a record of the symptoms is an important part of the diagnosis. This is because not every person reacts the same way. Some people have bacteria which do not produce hydrogen or have bacteria which use up the hydrogen and produce methane in the process. According to the most recent findings, it would also be necessary to measure the methane levels. But that is normally not done, cause the testing aparatus is evry expensive. If symptoms such as bloating, abdominal pain, diarrhoea etc. appear during the test or up to 12 hours after the breath test, then this is also a strong indication of intolerance. Please report such symptoms to your doctor.

The doctor concerned may additionally also measure the blood sugar levels (except fructose testing) during the breath testing period. If an intolerance is present then the tested sugar is not absorbed into the bloodstream, resulting in the blood sugar level remaining the same. If there is no existing intolerance, then the blood sugar level will rise because the sugar is being absorbed into the system.

most common breath tests

 Substance to be testedAmountBlow interval
Duration of the test
Lactose Intolerance Lactose 25-50 g 15 or 30 min 2 hours*
Fructose Malabsorption Fructose 25 g 15 or 30 min 2 hours*
SIBOS Glucose 50 g 10-20 min 3 hours
SIBOS Lactulose 10 g 10-20 min 3 hours
Sorbitol Intolerance Sorbitol 5-12 g approx. 20 min 3 hours

*If the values have risen above the basal level for a maximum of 10-20 ppm after 2 hours, the test should be extended to 4 hours

Practical Tips:

On the day of your test, take the day off! If you are intolerant, then you will spend a substantial part of the day in the most private room of the house – the toilet – and suffer from severe symptoms, because you will have ingested a high dosage of the very substance you cannot tolerate on an empty stomach!

Where possible, your doctor should also determine other blood values via a blood analysis (folic acid, B12, serum analysis, lipase, zinc and iron)

(1) Born Peter, World J Gastroenterol 2007 November 21;13(43): 5687-5691 "Carbohydrate malabsorption in patients with non-specific abdominal complaints"
2) Zechmann,M.; Masterman G., "Fruktoseintoleranz, Laktoseintoleranz und Histaminintoleranz: Erste Hilfe nach der Diagnose", Berenkamp Verlag, 1. Aufl 2012
3) Satish S.C. Rao, Ashok Attaluri, Leslie Anderson, Phyllis Stumbo; "Ability of the Normal Human Small Intestine to Absorb Fructose: Evaluation by Breath Testing"; Clinical Gastroenterology and Hepatology 2007;5:959–963
4) Mastropaolo, G., & Rees, W. D. (1987). Evaluation of the hydrogen breath test in man: definition and elimination of the early hydrogen peak. Gut, 28(6), 721–5.
5) Simrén, M., & Stotzer, P.-O. (2006). Use and abuse of hydrogen breath tests. Gut, 55(3), 297–303. doi:10.1136/gut.2005.075127
6) Yang, J.-F., Fox, M., Chu, H., Zheng, X., Long, Y.-Q., Pohl, D., … Dai, N. (2015). Four-sample lactose hydrogen breath test for diagnosis of lactose malabsorption in irritable bowel syndrome patients with diarrhea. World Journal of Gastroenterology, 21(24), 7563. doi:10.3748/wjg.v21.i24.7563
7) Methodology and Indications of H2-Breath Testing in Gastrointestinal Diseases: the Rome Consensus Conference. Alimentary Pharmacology & Therapeutics, 29: 1–49. 2009. doi:10.1111/j.1365-2036.2009.03951.x


Remember Me
Forgot username  Forgot password



Certifications & Quality

quality criteria logoThe information provided is created in compliance with a self-imposed quality management procedure


The information provided on the Food Intolerance Network website is no substitute for a visit to a registered dietician, nutritionist or a doctor. The information that you will find here may not be used as a substitute for professional advice and treatment by a medical professional or approved and registered dieticians. The content of the Food Intolerance Network website may not be used as a basis or means for any form of self-diagnosis.

Go to top