Description
Breath testing for Small Intestinal Bacterial Overgrowth (SIBO), measuring the gut bacterial fermentation products hydrogen and methane, is a robust method of assessing gut microbial activity. Breath gas production within 100 minutes of ingesting carbohydrates is diagnostic of SIBO.
Bacteria in the intestinal tract ferment ingested carbohydrates (lactulose is provided as an oral challenge for this test), gas byproducts pass across the gut wall into the circulation and are rapidly diffused by the lungs and exhaled in the breath.
Ambiguous gut symptoms following ingestion of foods, frequently diagnosed as Irritable Bowel Syndrome (IBS), have been associated with SIBO in up to 75% of these patients. The diagnostic method described here is largely unavailable in NHS gastroenterology departments because it’s considered a labour-intensive procedure for a chronic health condition.
Patients follow a strict low fermentable diet (low fibre, resistant starch, and complex carbohydrates) for 24 hours and fully fast for 12 hours (overnight) prior to the test to minimise normal colonic fermentation. Gas levels in a fasting breath sample are then compared against a subsequent nine samples collected at 20-minute intervals following ingestion of lactulose, a non-absorbable carbohydrate. Increases in breath hydrogen, methane, or both, within the first 100 minutes of the test period are indicative of small intestinal bacterial activity, subsequent gas production reflects normal bacterial activity in the large bowel.
The test results can also be used to assess colonic production of methane gas which occurs naturally in about a third of adults with increasing frequency by age, now formally recognised as Intestinal Methanogen Overgrowth (IMO).
Breath gas determination is also an approved method for the diagnosis of carbohydrate intolerances (specifically lactose and fructose).
