SIBO is diagnosed primarily by one of two methods: (1) collecting and culturing bacteria from the small intestine, and (2) hydrogen and methane breath test.

Endoscopy and Bacterial Culture

This somewhat invasive method involves passing a tube through the nose and down through the throat, esophagus, and stomach to reach the small intestine. X-ray is used to guide the sample collection. From the sample, the number of live bacteria are cultured and quantified. There, however, are several disadvantages of this method when compared to hydrogen breath testing. First, obtaining a sample from the small intestine is invasive and uncomfortable for the patient and is an expensive medical procedure. Moreover, the training required to collect a suitable sample for culturing is not common among medical professionals. Because quantitative culturing of bacteria is not routine is most medical settings, the accuracy of the results are often questionable. Finally, a limited number of samples can be collected using this method, increasing the likelihood that a sample may be collected from a location that does not contain the bacterial overgrowth.

Hydrogen and Methane Breath Test

Colonic bacteria are capable of consuming carbohydrates as food to provide energy. When these bacteria metabolize carbohydrates, they release the gases, carbon dioxide, hydrogen and methane, as waste products. The sorts of bacteria found in the small intestine, stomach, and esophagus produce very little gas. When we digest a meal, most of the carbohydrates are absorbed by the small intestine and never pass through to the colon. Additionally, more than 80% of the gas produced in the colon is consumed by other colonic bacteria. And so, normally, little gas remains in the colon. Some of this gas passes from the colon into the bloodstream, eventually entering the lungs, where it is expired through normal respiration. The concentration of these gases in a patient’s breath can be measured using sophisticated instrumentation, such as a gas chromatograph. This method has the advantage of being relatively inexpensive, accurate, and useful in determining the location of the infection.