SIBO can currently be tested using several methods, as listed below.

Breath Test

A glucose or lactulose breath test can be conducted to measure the hydrogen and/or methane produced by the bacteria in the small intestine after consuming the sugar solution. Some of these gases are then expired into the lungs, which can then be measured by the test. This is currently considered the most reliable and non-invasive  way to diagnose SIBO, and is by far the most common way to test for SIBO.  It can also be conducted at home or in-clinic, making it easily accessible.  Lactulose is non-absorbable and traverses the entire length of the small intestine, whereas glucose is absorbed in the first 2-3 feet of the intestine, so can only measure SIBO that is in the top section of the small intestine. It is for this reason that testing with both glucose and lactulose is often recommended for comprehensive results.  It is also recommended that the test is undertaken over a 3-hour period, with breath samples collected every 20 minutes, to measure the gas output over a longer transverse time.  Shorter tests can be conducted, but they may provide a false negative if the SIBO is present in the lower section of the small intestine. Fructose malabsorption can often be tested at the same time as a SIBO test to determine if fructose is problematic.

Small Intestine Culture

This can be performed by an endoscopy in-clinic, generally under anaesthesia.  This test is invasive and is not commonly used.

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