Diagnosing SIBO Using Breath Tests
Diagnosing SIBO Using Breath Tests

Diagnosing SIBO Using Breath Tests

By Sarah Bloor, Clinical GI Physiologist

What is SIBO?

Small Intestinal Bacterial Overgrowth (SIBO) is when there are too many bacteria in the small intestine. Usually, the small intestine has less than 1000 bacteria per mL of intestinal fluid, but in an individual with SIBO this is much greater – often over 100,000 bacteria per mL of intestinal fluid. This excessive colonisation of bacteria causes early fermentation of food to produce gases, such as hydrogen and methane. This leads to gut health symptoms, including bloating, abdominal pain, nausea and a change in bowel habit.

You may be thinking “but isn’t it normal to have lots of bacteria in my gut?”, and yes that is correct, but the bacteria should be mostly located in the colon, also known as the large intestine. The colon is home to trillions of bacteria, which play essential roles in breaking down the food we eat. In SIBO, these colonic bacteria move into the small intestine, meaning they break down the food before your body has the chance to digest it.

Diagnosing SIBO

SIBO is diagnosed most commonly via breath testing, which involves measuring intestinal gases in the breath. Gases produced in the intestines diffuse into the bloodstream, then circulation transports the gases to the lungs where they are excreted in the breath (Eisenmann et al., 2008).

Hydrogen gas in the body is solely produced via the bacterial fermentation of carbohydrates (Simren and Stotzer, 2006). During a SIBO breath test, a substrate is given, most commonly lactulose. Lactulose is a sugar that is indigestible to humans; therefore, it is not absorbed. Glucose can also be used; however, this is absorbed in the first 1/3rd of the small intestine leading to a higher chance of a false negative result if bacteria overgrow further along. Bacteria can ferment the lactulose or glucose, which produces hydrogen. How far into the study the hydrogen is produced allows us to determine if it is coming from bacterial fermentation in the small intestine (up to 90 minutes since ingestion), or the colon (after 90 minutes). This is reliant on the person being tested having normal transit time. However, as the body absorbs glucose, it rarely reaches the colon, so there is no peak after 90 minutes.

During a breath test, 10 breath samples are collected at 15-minute intervals. This may be extended if delayed transit time is suspected. We offer at-home breath test kits that you can perform at home, more information about our breath tests and how to perform them can be found here.

Once the breath test has been completed, your doctor/clinician will interpret your results and create a follow-up appointment to consult you on the next steps for your gut health.


AGIP, 2019. Association of Gastrointestinal Physiologists (AGIP) Proposed Standardised Testing Protocol for Hydrogen/Methane Breath Testing (HMBT) to Assess Small Intestinal Bacterial Overgrowth (SIBO) and Carbohydrate Malabsorption. Available at: <https://www.bsg.org.uk/wp-content/uploads/2019/12/AGIP-Best-Practice-Statement-for-HMBT_24.01.19.pdf> [Accessed 28 Apr. 2020].

Eisenmann, A., Amann, A., Said, M., Datta, B. and Ledochowski, M., 2008. Implementaion and interpretation of hydrogen breath tests. 2.

Gasbarrini, A., Corazza, G.R. and Gasbarrini, G., 2009. Methodology and Indications of H2-Breath Testing in Gastrointestinal Diseases: the Rome Consensus Conference. Alimentary Pharmacology & Therapeutics, 29(s1), pp.1–49.

Paterson, W., Camilleri, M., Simren, M., Boeckxstaens, G. and Vanner, S.J., 2017. Breath Testing Consensus Guidelines for SIBO: RES IPSA LOCQUITOR. Official journal of the American College of Gastroenterology | ACG, 112(12), pp.1888–1889.

Rezaie, A., Buresi, M., Lembo, A., Lin, H., McCallum, R., Rao, S., Schmulson, M., Valdovinos, M., Zakko, S. and Pimentel, M., 2017. Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus. Am J Gastroenterol, 112(5), pp.775–784.

Simren, M. and Stotzer, P.O., 2006. Use and abuse of hydrogen breath tests. Gut, 55(3), pp.297–303.