SIBO can be diagnosed with breath tests or a duodenal aspirate culture (a lab test done on a small fluid sample from the small intestine), but the lack of standardization makes accurate diagnosis challenging. Breath tests are an indirect way to measure bacteria in the small intestine, but their ease and low invasiveness make them a more common diagnostic tool than the fluid test.[1][2]
During a breath test, the patient ingests a carbohydrate — usually glucose or lactulose — which is fermented by bacteria in the small intestine. The bacteria produce hydrogen and methane, which are expelled and measured in the patient’s exhaled breath. (Hydrogen sulfide is also produced, but only in recent years has it been added to some tests.) The quantity and production rate of these gasses can then be used to estimate the number of microbes in the small intestine, because gut microbes are the only source of hydrogen and methane. However, many factors, including the way the test is administered, can affect the results and lead to a false positive or false negative diagnosis, so these tests are likely to be less accurate than the duodenal culture method.[1][2]
Sampling contents from the duodenum, a section of the small intestine, is a more direct way to measure the bacteria, but it’s highly invasive. This test requires intubating the patient, which involves inserting a tube into their throat and routing it through their stomach to reach the first section of their small intestine, where the clinician will aspirate (suction out) multiple samples of liquid. Swabs of the liquid are applied to cell culture plates that support the growth of many (but not all) types of bacteria in that sample, and the bacteria are eventually counted. Culturing methods could lead to false positives or false negatives due to sample contamination or improper growth conditions, respectively.[1][2]
Clinicians have yet to reach a consensus on diagnostic criteria for a positive result of either test, but it’s generally accepted that SIBO is present when there is a concentration of 103–105 colony forming units per milliliter (CFU/mL) in a fluid sample. However, some researchers or clinicians consider that number to be greater than 10^5 CFU/mL.[1][2]
References
- ^Ali Rezaie, Michelle Buresi, Anthony Lembo, Henry Lin, Richard McCallum, Satish Rao, Max Schmulson, Miguel Valdovinos, Salam Zakko, Mark PimentelHydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American ConsensusAm J Gastroenterol.(2017 May)
- ^Giuseppe Losurdo, Gioacchino Leandro, Enzo Ierardi, Francesco Perri, Michele Barone, Mariabeatrice Principi, Alfredo Di LeoBreath Tests for the Non-invasive Diagnosis of Small Intestinal Bacterial Overgrowth: A Systematic Review With Meta-analysisJ Neurogastroenterol Motil.(2020 Jan 30)