Breath testing for Digestive Problems: Pros and Cons
October 15, 2024
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Breath testing for Digestive Problems: Pros and Cons
- By Sharon Erdrich
- Digestive Health, Gut Health Blog
Hydrogen-methane breath testing is currently the most popular method used to diagnose small intestinal bacterial overgrowth (SIBO) and intestinal methanogen overgrowth (IMO).
SIBO occurs when bacteria that are typically found in the colon occupy, and proliferate in the small intestine, leading to symptoms such as bloating, abdominal pain, flatulence, and diarrhoea or constipation.
IMO, on the other hand, occurs due to overgrowth of organisms that produce methane – which can occur anywhere in the gut – and is closely linked with symptoms like constipation, bloating, and gas.
While it is possible to diagnose SIBO through (invasive, expensive and seldom-done) small bowel aspiration or breath testing, IMO is solely diagnosed through breath testing, making this an essential diagnostic tool.
Breath testing for SIBO and IMO is non-invasive, simple, and widely accessible, with the option to complete tests at home. The process involves following pre-test instructions, then on the day of testing, consuming a carbohydrate substrate (see below) and capturing samples of exhaled breath. These samples are used to measure the levels of hydrogen and methane gas. These gases are produced by the bacteria and archaea present in the gut when they ferment carbohydrates, and they get absorbed into the bloodstream and are quickly exhaled on breath.
Increased concentrations of hydrogen within a short time-frame suggest SIBO, while elevated methane (at any time) indicates IMO.
Breath tests also offer the ability to guide treatment plans based on the results, tailoring therapies to the specific type of microbial overgrowth.
Despite its widespread use, breath testing has some limitations. One of the main criticisms is that it provides only an indirect measure of microbial overgrowth, relying on gas production as a proxy for bacterial counts. Additionally, variability in the time it takes for food to move from the mouth to the small intestine (oro-caecal transit time) can affect the accuracy of the test. Rapid transit can lead to false-positive results, while slow transit can result in false negatives, making test interpretation challenging in some cases.
Other factors, such as compliance with pre-test protocols (e.g., avoiding certain foods, medications, or activities), can also influence test results.
Several different types of breath tests are available, with glucose, fructose, and lactulose being the most common substrates used. Each has its pros and cons.
- Glucose breath testing is considered very specific for SIBO, as glucose is absorbed quickly in the small intestine and is less likely to cause false positives due to fermentation in the colon. However, because of this rapid absorption, it may also result in false negative (because the glucose was absorbed before bacteria could ferment it).
- Fructose can detect SIBO, IMO and fructose malabsorption. Fructose it normally slower to be absorbed (especially when consumed without glucose), thus may reach further down the small intestine than glucose. Any increase in gases on fructose testing is abnormal, and needs careful interpretation.
- Lactulose can provide a “readout” of fermentation in the entire small intestine, potentially identifying distal SIBO that glucose might miss. However, it can result in false positives due to rapid transit (as explained above), or false negatives if the bacteria present can not ferment this complex sugar molecule.
Each test has its place, and a more complete picture can be obtained by conducting all three tests, depending on the presenting problems and the judgement of the prescribing clinician. Other testing substrates can also be used, for example lactose (to diagnose lactose intolerance), sugar, mannitol or sorbitol, depending on the problems and discretion of the prescribing clinician.
One of the significant strengths of breath testing is its ability to guide treatment decisions. Understanding the gas patterns, and when they are produced during the breath test allows clinicians to tailor treatments more effectively, potentially improving outcomes.
Breath testing has been particularly useful in managing conditions like irritable bowel syndrome (IBS), where there is overlap with SIBO and IMO. Studies have shown that IBS patients with positive breath tests for SIBO often experience symptom relief with antimicrobial treatment. Similarly, IMO has been linked to constipation-predominant IBS, and treating the overgrowth of methanogens has been shown to reduce constipation severity.
Elevated methane, in addition to being linked to constipation and overweight, is also associated with diverticulitis and delayed gastrointestinal transit time.
There are, however, some limitations to breath testing that clinicians must be aware of. For instance, false negatives can occur if the carbohydrate substrate does not reach the affected part of the intestine due to conditions like gastroparesis or achalasia, which impair gastrointestinal motility. Additionally, in cases where methane-producing organisms dominate, hydrogen levels may be suppressed, leading to an underestimation of bacterial overgrowth. In these scenarios, responses to treatment may not go as expected, and alternative approaches may be necessary.
Another challenge in breath testing is the variability of test patterns and the need for emerging research to better understand these patterns. Flat-line patterns, characterised by low or no gas production, have been associated with conditions like inflammatory bowel disease (IBD) and may indicate the presence of bacteria that consume hydrogen.
The ratio of breath methane-to-hydrogen has also been proposed as an indicator of gut dysbiosis. In one study this was significantly associated with cancer of the head and neck.
High baseline hydrogen levels, on the other hand, could indicate overgrowth even in fasting conditions, suggesting a more severe or chronic form of SIBO. Certainly more research is needed to improve test interpretation, diagnostic accuracy and treatment strategies based on breath test results.
In the diagnosis of IMO, breath testing remains the most accurate method available in clinical practice. Methanogens detected in stool tend not to give a representation of the true extent of the problem.
Knowing that methane is elevated can help fine-tune the management of gut problems such as constipation, which is strongly associated with IMO.
In conclusion, while breath testing is not without its limitations, it is certainly a valuable tool in the diagnosis and management of SIBO and IMO. Its non-invasive nature, accessibility, and ability to guide treatment decisions make it a preferred diagnostic method for many. With ongoing research into new breath test patterns and emerging diagnostic technologies, breath testing will likely continue to play a crucial role in the management of digestive problems for some time.
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References
Gottlieb, K. et al. Selection of a cut-off for high- and low-methane producers using a spot-methane breath test: Results from a large North American dataset of hydrogen, methane and carbon dioxide measurements in breath. Gastroenterol. Rep. (Oxf) 5, 193–199.
Jang SI, et al. Relationship between intestinal gas and the development of right colonic diverticula. J Neurogastroenterol Motil. 2010 Oct;16(4):418-23.
Lim J, Rezaie A. Pros and Cons of Breath Testing for Small Intestinal Bacterial Overgrowth and Intestinal Methanogen Overgrowth. Gastroenterol Hepatol (N Y). 2023 Mar;19(3):140-146.
Simrén M, et al. Management of the multiple symptoms of irritable bowel syndrome. Lancet Gastroenterol Hepatol. 2017 Feb;2(2):112-122.
Suri, J. et al. Elevated methane levels in small intestinal bacterial overgrowth suggests delayed small bowel and colonic transit. Medicine (Baltimore) 2018. 97, e10554.
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