Hydrogen and methane breath testing (HMBT) is a non-invasive diagnostic tool frequently used to assess small intestinal bacterial overgrowth (SIBO) and carbohydrate malabsorption disorders such as lactose and fructose intolerance. Despite its widespread use in adults, its application in children is less standardized, and clinicians often face uncertainties about adapting adult protocols for the pediatric population.
This article discusses the use of HMBT in children, highlights the key considerations for interpreting results, and reflects on the most reliable available guidelines, particularly the 2017 North American Consensus.
Background and Current Challenges:
SIBO, as well as carbohydrate malabsorption such as lactose and fructose intolerance, can cause gastrointestinal symptoms in both children and adults, such as bloating, diarrhoea, abdominal pain, and malnutrition. In children, nutritional deficiencies leading to failure to thrive pose a great challenge in paediatric clinics. Since children require a constant supply of nutrients for healthy growth, accurate diagnosis is especially crucial in this age group. Despite the seriousness of the need for HMBTs in children, the literature is extremely sparse for this age group, and testing clinics have to rely on the more robust adult consensus guidelines. When applying adult HMBT protocols to children, there are significant challenges due to differences in gut physiology, metabolic rates, and transit times.
While the European Society for Paediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) has issued guidelines for paediatric breath testing, there are limitations, including inconsistencies in test performance, lack of paediatric-specific threshold values, and variability in interpreting test results. This has led to hesitancy in fully endorsing these guidelines for clinical use. Instead, many experts, including myself, recommend following the 2017 North American Consensus guidelines, even though these were primarily designed for adults. The North American Consensus offers more robust guidance that can be adapted for paediatric use with careful consideration.
Test Protocols and Dosages for Children:
Despite the absence of paediatric-specific guidelines, one of the most reliable approaches is to use the same substrates and dosages as those recommended for adults. For instance, the North American Consensus suggests using:
- Lactulose: 10 g or 15 mL for diagnosing SIBO.
- Lactose or fructose: 25 g for diagnosing intolerance.
It is important to note that while these dosages are appropriate for adults, they may be on the higher side for children. For example, a 25 g dose of lactose is roughly equivalent to consuming 500 mL of milk, which can be excessive for a child and may lead to false positives. Therefore, clinicians should be cautious in interpreting positive results and should always consider the child’s ability to absorb such quantities.
Moreover, similar to adults, for children, it is particularly important to prioritise ruling out SIBO before testing for intolerance. SIBO can cause secondary malabsorption and intolerance, meaning that treating SIBO could resolve carbohydrate intolerance symptoms. This is of utmost importance in the paediatric age group, as diagnosing lactose intolerance entails significant restrictions on the essential nutrients required for the healthy growth of children.
SIBO Testing and the Role of Methane:
When testing for SIBO, lactulose is typically used as the substrate. Lactulose is a non-absorbable sugar, and the bacteria in the small intestine ferment it, producing hydrogen (H2) and methane (CH4). The consensus suggests using a 20 ppm rise in H2 from the baseline as the threshold for diagnosing SIBO. While this threshold was established for adults, it is also a conservative measure that can be applied to paediatric populations. It is conservative in the sense that if the test is negative for SIBO, despite the intake of adult-dose lactulose, SIBO is ruled out. A positive result for SIBO in children may be due to a quick oro-caecal transit, due to the shorter length of the GI tract or faster gut motility. Therefore, a positive result is inconclusive unless a paediatric oro-caecal transit study confirms the timing of lactulose transit in that particular patient for interpretation.
Methane Detection in Children: Thresholds, Prevalence, and Clinical Implications:
CH4 detection is an essential aspect of HMBT, particularly for identifying intestinal methanogen overgrowth (IMO). CH4 production has been linked to slower gastrointestinal motility, contributing to symptoms such as constipation, a common issue in children with IMO. Elevated CH4 levels not only indicate the presence of methanogenic flora but also highlight the need for targeted therapies that can alleviate gastrointestinal symptoms like bloating, abdominal discomfort, and malabsorption, particularly in children where growth and nutrient absorption are crucial.
One significant factor in interpreting CH4 breath test results in children is the role of oro-caecal transit time, which does not appear to impact CH4 analysis. Unlike H2 production, which can be influenced by rapid oro-caecal transit, CH4 detection is independent of how quickly food passes through the small intestine. This means that CH4 breath test results are less prone to false positives or negatives caused by variations in gut transit time, making them a reliable tool in both adult and paediatric populations.
However, when discussing CH4 thresholds, it is important to acknowledge the difference in the prevalence of methanogens between children and adults. Studies, including one by Vanderhaeghen et al. (2015), have shown that children generally have a lower prevalence of methanogens such as Methanobrevibacter smithii. In their study, 65% of children had detectable levels of methanogens, compared to 89% of adults, and the relative abundance of methanogens in children was lower (0.15% vs. 0.52%).
While the prevalence of methanogens is lower in children, this does not necessarily imply that CH4 production is consistently low in those who carry methanogens. Children with detectable methanogens may still produce CH4 at levels comparable to adults, as the metabolic activity of Methanobrevibacter smithii and related species is primarily driven by substrate availability rather than just the prevalence of the species. This means that while fewer children may test positive for CH4, those who do could produce significant amounts of CH4. However, the same article provides a very interesting insight into the relative abundance of Methanobacteriales in children that was significantly lower compared to adults (0.15% in children vs 0.52% in adults). This difference indicates that children who are positive for hosting methanogenic species may naturally produce less CH4, and using adult thresholds might lead to underdiagnosis. Therefore, using the 10 ppm threshold for CH4 in children could be considered a conservative measure, ensuring that cases of methanogen overgrowth are not over-diagnosed with the adult threshold for CH4 production.
Given this data, it seems prudent to maintain the adult threshold of 10 ppm for CH4 in children. This threshold is less prone to false positives in children. A positive result in children can be confidently interpreted as evidence of CH4 overproduction and potentially linked to conditions like IMO. However, a negative result may still leave some uncertainty, as the lower prevalence of methanogens in children might mean that the absence of detectable CH4 does not entirely rule out the possibility of overgrowth in a child with low but metabolically active methanogenic populations.
Lactose and Fructose Intolerance Testing:
Once SIBO or IMO has been ruled out, testing for lactose and fructose intolerance can proceed. The same substrates used in adult testing—25 g of lactose or fructose—may be used in children. Nevertheless, because of shorter oro-caecal transit times in children, there is a greater chance of obtaining false-positive results.
Clinicians should be mindful of the fact that a 25 g dose of lactose or fructose might exceed the typical absorption capacity for a child. This also could lead to false-positive test results that do not necessarily reflect the child’s usual dietary intake, which may only involve smaller quantities of these sugars.
A negative result is generally more reliable despite the intake of a high adult dose of substrates and the increased chance of quick oro-caecal transit or reduced absorption capacity in children.
Oro-Caecal Transit Time and Confirmation of Results:
One of the complexities in interpreting breath test results, especially in children, is determining whether a rise in H2 or CH4 is truly indicative of SIBO or simply reflects normal oro-caecal transit.
Scintigraphy can be used to confirm the oro-caecal transit time, and clinicians should ensure that the time to reach the caecum matches the expected timing seen in the breath test. This step can help prevent false positives and improve the accuracy of the diagnosis.
Limitations of Alternative Tests for Lactose Intolerance Compared to HMBT:
Another alternative way to test lactose intolerance is genetic testing (LCT gene), some clinicians may consider an LCT gene or intestinal biopsy for lactose intolerance. While genetic testing can be useful, particularly for identifying congenital lactase deficiency (CLD), it has limitations. Acquired lactose intolerance, which is the most common form, is not uniformly detectable through genetic testing because lactase production can vary along the intestinal lining. A biopsy, similarly, may yield false-negative or false-positive results depending on where the sample is taken. LCT has no value in monitoring response to treatment or dietary changes. It is also important to note that not all individuals with a positive LCT test are intolerant to lactose in real life.
An alternative diagnostic method is the lactose tolerance test (LTT), which involves measuring blood glucose levels after lactose ingestion. If lactose is properly digested, blood glucose levels should rise. However, this test has not been standardised for children, and there is considerable variability in how it is performed and interpreted, making it less reliable than breath testing in paediatric populations.
HMBT offers several advantages over these methods. Breath testing provides a non-invasive way to directly measure the presence of H2 and CH4 gases produced by the fermentation of undigested lactose in the colon. This method is particularly effective because it can detect lactose malabsorption regardless of its cause, whether congenital or acquired. Additionally, breath testing allows for monitoring of response to treatment or dietary changes, offering a more comprehensive approach to managing lactose intolerance.
Conclusion and Future Directions:
HMBT remains one of the most reliable diagnostic tools for assessing SIBO and carbohydrate malabsorption. While there is no definitive paediatric protocol, the North American Consensus guidelines provide a solid foundation for adapting adult protocols to younger patients.
Clinicians should exercise caution when interpreting positive results, especially in cases where substrate doses may be too high for children or where faster oro-caecal transit times could result in false positives. In all cases, ruling out SIBO or IMO should be the first step, as treating these underlying conditions can often resolve symptoms of intolerance.
HMBT remains the most practical approach for diagnosing SIBO and carbohydrate malabsorption in paediatric patients. However, more research is needed to refine protocols, establish paediatric-specific thresholds, and improve the accuracy of testing and interpretation in this vulnerable population.
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References:
- Rezaie, A., et al. (2017). «Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus.» American Journal of Gastroenterology, 112(5), 775-784.
- Di Lorenzo, C., et al. (2019). «Gastrointestinal Motility in Children.» Journal of Pediatric Gastroenterology and Nutrition, 68(6), 759-770.
- Furnari, M., et al. (2018). «Breath Tests for Small Intestinal Bacterial Overgrowth: A Comprehensive Review.» Gut and Liver, 12(4), 403-412.
- He, T., et al. (2017). «Lactose Intolerance and Genetic Testing: An Overview.» European Journal of Pediatrics, 176(8), 1113-1121.
- Szajewska, H., et al. (2018). «Lactose Intolerance in Children: A Position Paper by the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN).» Journal of Pediatric Gastroenterology and Nutrition, 66(1), 165-174.
- Vanderhaeghen, S., Lacroix, C., & Schwab, C. (2015). «Methanogen communities in stools of humans of different age and health status and co-occurrence with bacteria.» FEMS Microbiology Letters, 362(13), fnv092.
- Ghali, M. B., et al. (2017). «Gut methanogens: Methanobrevibacter smithii and health in children and adults.» Journals of Microbiology.
- Nature Reviews Microbiology. (2017). «The gut microbiome and its role in health and disease».
