Small Intestinal Bacterial Overgrowth (SIBO) is a digestive health condition characterized by an abnormal increase in the bacterial population within the small intestine. The small intestine is not typically home to a large number of bacteria. When microbes from the large intestine migrate upward, they can interfere with digestion and nutrient absorption. This overgrowth leads to uncomfortable gastrointestinal symptoms, such as bloating, abdominal discomfort, and gas. To confirm SIBO, the SIBO breath test is the primary non-invasive method used to assess bacterial activity in the gut.
Understanding the SIBO Breath Test
The SIBO breath test is the standard, non-invasive method for evaluating bacterial overgrowth in the small intestine. The test operates on the principle of measuring specific gases produced by bacteria. When bacteria consume carbohydrates, they release byproducts, primarily gas, through fermentation.
The two main gases measured are hydrogen and methane, produced by different types of microorganisms, specifically bacteria and archaea, that inhabit the gut. Humans do not produce these gases naturally, meaning their presence in the breath indicates microbial activity. Approximately 20% of the gas produced in the intestines is absorbed into the bloodstream, travels to the lungs, and is then exhaled. The test quantifies the parts per million (ppm) of these gases in timed breath samples.
Preparing for Accurate Results
Accurate SIBO breath test results rely heavily on strict adherence to preparatory instructions, as non-compliance can lead to misleading or uninterpretable data. This preparation aims to “starve” the intestinal bacteria before the test, ensuring that the only fermentable material they encounter is the substrate provided during the procedure.
The first step involves a specific, low-residue diet, often referred to as the “prep diet,” which must be followed for 24 hours before the test. This diet strictly limits all sources of complex carbohydrates, fiber, and sugars, which are the primary food sources for intestinal bacteria. Acceptable foods include plain, steamed white rice, baked or broiled fish or poultry seasoned only with salt and pepper, eggs, and clear meat broth. All fruits, vegetables, grains, and dairy products are avoided.
The next step is the cessation of specific medications and supplements that could alter the gut microbiome or intestinal motility. Antibiotics and antifungals must be discontinued for a minimum of two weeks prior to testing. Probiotics, prebiotics, laxatives, and motility-influencing drugs should be stopped at least one week before the procedure. Over-the-counter items like antacids and proton pump inhibitors (PPIs) may need to be temporarily held, as they can influence the bacterial environment.
Finally, a mandatory fasting period is required immediately before the test, typically lasting 12 hours. During this time, only water is permitted. The patient must also refrain from activities like smoking or vigorous exercise for at least one hour before and during the test, as these can affect breath composition.
Step-by-Step Testing Procedure
The SIBO breath test procedure is a timed, multi-step process that can be performed in a clinic or at home using a specialized collection kit. The test begins with the collection of a baseline breath sample, taken before any substrate is consumed, to establish the patient’s starting levels of hydrogen and methane. This initial sample is necessary for comparison, ensuring that the fermentation activity measured later is in response to the test solution.
Following the baseline collection, the patient ingests a precisely measured amount of a sugar solution, known as the substrate. The two most common substrates used are lactulose and glucose, each providing different diagnostic insights. Glucose is rapidly absorbed in the upper portion of the small intestine, making it better for detecting overgrowth in the proximal gut. Lactulose is a non-digestible sugar that travels the entire length of the small intestine, allowing it to detect overgrowth in the distal segments.
After drinking the substrate, breath samples are collected at regular, timed intervals, usually every 15 to 20 minutes, over a period of two to three hours. These intervals track the substrate’s transit through the digestive system, allowing practitioners to pinpoint where fermentation is occurring. As the solution moves through the small intestine, any abnormal concentration of bacteria will ferment the sugar, producing hydrogen and methane gas. The timing of the gas rise is an indicator, as a rapid increase suggests fermentation is happening early in the small intestine, which is consistent with SIBO.
Decoding the Results
The interpretation of the SIBO breath test relies on analyzing the pattern of gas levels over the testing period, specifically looking for a significant and early increase in hydrogen or methane.
A result is considered positive for hydrogen-predominant SIBO if there is a rise of 20 parts per million (ppm) or more above the baseline hydrogen level within the first 90 minutes of the test. This early rise indicates that the substrate was fermented before it reached the large intestine, confirming the presence of an overgrowth in the small bowel.
For methane, the established threshold for a positive result is a level of 10 ppm at any point during the entire test, which suggests the presence of methane-producing archaea. It is possible to test positive for both gases, which is sometimes seen when methanogens consume the hydrogen produced by other bacteria to create methane. The distinction between hydrogen and methane predominance is important because it guides subsequent treatment strategies. Once a diagnosis of SIBO is confirmed, the next step involves consulting a healthcare provider to develop a personalized treatment plan.