SIBO Diagnosis: Lactulose Testing
1. What is SIBO?
1.1 SIBO Diagnosis
1.2 SIBO Treatment
2. Lactulose Testing
2.1 Procedure of the Lactulose Breath Test
2.2 Interpretation of the Lactulose Breath Test
2.3 Advantages and Disadvantages of the Lactulose Breath Test
2.4 Summary of the Lactulose Breath Test
1. What is SIBO?
SIBO, short for Small Intestinal Bacterial Overgrowth, is a common condition increasingly seen in gut clinics, especially in urban centers like London, where many IBS patients seek help. If you experience recurring abdominal pain, bloating, diarrhea or constipation you may be dealing with more than just regular digestive discomfort.
SIBO is often linked to imbalances in the digestive system that disrupt normal gut function. Although the gut normally houses bacteria—especially in the colon—SIBO involves excessive bacterial growth in areas where it shouldn’t dominate. This bacterial overactivity can include the overproduction of gases and toxins, which are responsible for uncomfortable symptoms such as pain, bloating, and irregular bowel movements.
1.1 SIBO Diagnosis
A breath test is a widely used diagnostic tool in gastroenterology clinics, especially for identifying SIBO. If you struggle with unexplained digestive issues, this simple, non-invasive test may help.
The test measures hydrogen (H₂) and methane (CH₄) in your exhaled air. Since human cells do not naturally produce these gases, their presence is a strong link to bacterial fermentation. During the test, various sugars—such as lactulose, lactose, glucose, or fructose—are consumed.
When bacteria metabolize these sugars, they produce gases that travel through the blood to the lungs and are then exhaled. The breath test is commonly used by leading doctors who specialize in IBS and other gut conditions.
1.2 SIBO Treatment
There are several approaches used in gut health clinics to manage and treat SIBO. If you are diagnosed with SIBO, you may be recommended a personalized diet plan that includes a low-FODMAP or targeted probiotics, or specific herbal antimicrobials.
Instead of a one-size-fits-all method, the choice of therapy is based on the dominant bacterial type and the pattern of your symptoms. Supervision by leading doctors in gastroenterology or an experienced naturopath ensures that your care plan aligns with your body’s needs.
In top London clinics, these personalized approaches may also include microbiome testing and symptom tracking to optimize outcomes. Whether addressing gas, diarrhea, discomfort, or recurring gut conditions, the right support can help you return to a more regular, healthy routine.
2. Lactulose Testing
Lactulose is a disaccharide composed of galactose and fructose. Since the human body cannot digest lactulose, it is particularly useful for assessing bacterial activity throughout the entire small intestine (2).
2.1 Procedure of the Lactulose Breath Test
The lactulose breath test is a widely used diagnostic tool for detecting SIBO in specialized gut clinics, especially in London and other urban health hubs. The procedure starts with the patient providing a fasting breath sample. Afterwards, they drink a test solution containing 10g of lactulose, dissolved in 200–250 ml of water (1). Breath samples are then collected at regular intervals—every 15 to 20 minutes—over a period of approximately three hours. This method is often recommended by doctors and specialists in gastroenterology to investigate persistent IBS-like symptoms such as abdominal pain, bloating, and diarrhea.
2.2 Interpretation of the Lactulose Breath Test
A positive result in the breath test is typically defined by a rise in hydrogen (H₂) of more than 20 ppm within the first 90–100 minutes, or the appearance of a double peak in hydrogen output. The first peak is linked to SIBO, indicating an overgrowth of bacteria that disrupts normal gut function—frequently seen in patients suffering from common conditions like IBS. The second peak is usually associated with the natural fermentation of lactulose further along in the digestive process (2).
A delayed rise in gas after 100–120 minutes is considered a normal response and not necessarily proof of SIBO. However, an increase in methane (CH₄) by over 10 ppm compared to the baseline can also indicate bacterial imbalance. You may experience symptoms even in borderline cases, so working closely with experienced doctors is essential.
If no overgrowth is present, lactulose typically reaches the colon without early fermentation (2). A lack of hydrogen or methane response within the first 100–120 minutes often suggests that SIBO is not the cause of the gut issues. In this situation, gases are only detected later, when colonic bacteria begin fermenting the lactulose, leading to a secondary, low-level gas increase.
2.3 Advantages and Disadvantages of the Lactulose Breath Test
The lactulose breath test is a widely used, non-invasive tool for identifying SIBO, a common cause of chronic gut conditions like IBS, bloating, and abdominal pain. In many European countries, including Germany, the glucose breath test is preferred by some clinics, but lactulose remains a cost-effective and accessible option. Compared to procedures like endoscopy, breath testing is much more convenient for patients.
However, there are some limitations. The accuracy of this test can vary between studies. One challenge is that lactulose can act as a mild laxative, speeding up digestion and potentially skewing the timing of gas production. As a result, the test’s sensitivity ranges from 17% to 68%, and specificity varies between 44% and 86% (2).
Another known limitation is related to specific bacterial species. If a patient’s gut is primarily colonized by gram-negative bacteria such as Escherichia coli or Klebsiella, Citrobacter and Haemophilus which do not ferment lactulose, the result may appear false-negative—even if SIBO is present. That’s why doctors in advanced gastroenterology clinics may recommend complementary diagnostics, nutritional support, or even a probiotic protocol alongside low-FODMAP dietary guidance.
2.4 Summary of the Lactulose Breath Test
To summarize, the lactulose breath test is a simple, widely used method for identifying bacterial imbalances in the gut, especially in SIBO-related cases. While it has both strengths and limitations, it remains a go-to diagnostic tool in many leading gut clinics.
If you are struggling with regular digestive symptoms such as bloating, diarrhea, or abdominal discomfort, a breath test—combined with expert support from gastroenterology doctors—can provide valuable insight. You may also benefit from individualized nutrition advice or a targeted probiotic program to support long-term gut health. For an optimal interpretation of the results the preparation of the breath test is key.
References
- 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.
- 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.
- 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.
