SIBO Diagnosis: Glucose Testing
1. What is SIBO?
1.1 SIBO Diagnosis
1.2 SIBO Treatment
2. Glucose Breath Test
2.1 Procedure of the Glucose Test
2.2 Interpretation of the Glucose Test
2.3 Advantages and Disadvantages of the Glucose Test
2.4 Summary
1. What is SIBO?
Small Intestinal Bacterial Overgrowth (SIBO) refers to an unusual proliferation of bacteria in the small intestine, which is normally low in bacterial content. This bacterial imbalance can cause significant digestive distress, such as abdominal pain, bloating, diarrhea, constipation, and even lactose intolerance in some cases. These symptoms often mimic those of IBS, which is why SIBO is sometimes misdiagnosed.
The overgrowth results in excessive fermentation of carbohydrates, leading to gas production and toxin accumulation in the bowel. Unlike the large intestine—where such processes are natural—the gut environment in the small intestine is more delicate and easily disrupted by microbial imbalance.
1.1 SIBO Diagnosis
The most accurate method for SIBO diagnosis is the hydrogen breath test, often referred to as a SIBO breath test in clinical settings. At a clinic or specialized healthcare facility, the patient is given a test solution containing substances such as lactulose, lactose, glucose, or fructose.(1)
After drinking the solution, the bacteria in the small intestine ferment the sugars, producing hydrogen or methane gas. These gases are absorbed into the bloodstream and later exhaled. The patient provides breath samples over several hours, which are analyzed for gas levels.
Because human cells don’t produce hydrogen or methane, elevated levels in the breath indicate bacterial fermentation. The timing and intensity of this gas release help clinicians determine the presence and severity of SIBO.
1.2 SIBO Treatment
SIBO treatment varies depending on the individual case but typically involves:
antibiotics to reduce bacterial overgrowth, probiotics to rebalance the microbiome, a personalized diet, often following a low-FODMAP protocol. Some healthcare providers also recommend avoiding products that worsen symptoms, such as high-FODMAP foods or poorly absorbed carbohydrates. A tailored plan should be created by a clinic or gastroenterology professional, and regular follow-up is essential.
2. Glucose Breath Test
In Germany, the glucose breath test has become the recognized standard (as of March 2024) for detecting hydrogen production in SIBO. It is commonly used in clinic environments to diagnose gut imbalances early.
2.1 Procedure of the Glucose Test
The glucose breath test is a widely used method in clinics and healthcare facilities to diagnose SIBO (Small Intestinal Bacterial Overgrowth). To begin, the patient provides a fasting breath sample. Then, a test solution containing 75g of glucose dissolved in 250ml of water is administered (1,2).
Afterward, breath samples are collected at regular intervals (every 15 to 20 minutes) over the course of 2–3 hours. This allows clinicians to monitor gas levels—especially hydrogen and methane—which are key indicators of gut fermentation activity linked to bacterial overgrowth.
2.2 Interpretation of the Glucose Test
A positive result typically occurs when hydrogen gas levels rise above 20 ppm within the first 90 minutes (2,3). Since human cells do not produce hydrogen or methane, a significant increase indicates fermentation by bacteria in the small intestine—confirming a SIBO diagnosis via hydrogen breath testing.
This type of sibo breath test is considered non-invasive, cost-effective, and widely accessible, making it a preferred option in modern digestive healthcare settings.
2.3 Advantages and Disadvantages of the Glucose Test
Glucose is a monosaccharide carbohydrate and a fast-absorbing energy source. While this makes it suitable for early detection of proximal gut issues, it also means the glucose is quickly absorbed in the upper bowel, limiting the test’s ability to detect SIBO in the distal small intestine.
Compared to the lactulose test, which can track fermentation in later intestinal segments, the glucose test may miss certain overgrowth cases. Additionally, since it doesn’t typically cause reactions in patients with lactose intolerance, it may be a better option for those sensitive to other sugars like lactose.
Despite these limitations, the glucose test is widely used for identifying abdominal symptoms such as bloating, IBS-like discomfort, and unexplained digestive issues caused by bacteria fermenting carbohydrates.
Sensitivity ranges from 20% to 93%, and specificity ranges from 30% to 86%, depending on how well the sample collection, preparation, and breath levels are monitored. (4).
2.4 Summary
In summary, the glucose hydrogen breath test is a simple, well-tolerated method for detecting SIBO. It provides useful insights into digestive health and helps guide treatment options. For optimal results, it’s crucial for patients to follow all instructions regarding test preparation, dietary restrictions, and breath sample timing during the hours of testing.
References
- Saad RJ, Chey WD. Breath testing for small intestinal bacterial overgrowth: maximizing test accuracy. Clin Gastroenterol Hepatol. 2014 Dec;12(12):1964-72; quiz e119-20. doi: 10.1016/j.cgh.2013.09.055. Epub 2013 Oct 1. PMID: 24095975.
- Hammer HF, Fox MR, Keller J, Salvatore S, Basilisco G, Hammer J, Lopetuso L, Benninga M, Borrelli O, Dumitrascu D, Hauser B, Herszenyi L, Nakov R, Pohl D, Thapar N, Sonyi M; European H2-CH4-breath test group. European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus. United European Gastroenterol J. 2022 Feb;10(1):15-40. doi: 10.1002/ueg2.12133. Epub 2021 Aug 25. PMID: 34431620; PMCID: PMC8830282.
- Massey BT, Wald A. Small Intestinal Bacterial Overgrowth Syndrome: A Guide for the Appropriate Use of Breath Testing. Dig Dis Sci. 2021 Feb;66(2):338-347. doi: 10.1007/s10620-020-06623-6. Epub 2020 Oct 10. PMID: 33037967.
- Rezaie A, Buresi M, Lembo A, Lin H, McCallum R, Rao S, Schmulson M, Valdovinos M, Zakko S, Pimentel M. Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus. Am J Gastroenterol. 2017 May;112(5):775-784. doi: 10.1038/ajg.2017.46. Epub 2017 Mar 21. PMID: 28323273; PMCID: PMC5418558.
