Hydrogen Methane Breath Test is a test to diagnose gastrointestinal disorders by measuring the change in hydrogen concentration in the breath after oral administration of a compound. It is commonly used to detect gastrointestinal motility and also to diagnose bacterial overgrowth in the small intestine. Methane hydrogen breath test is widely used in the detection of various gastrointestinal diseases, such as chronic diarrhea, chronic constipation, functional dyspepsia, irritable bowel syndrome, gastrointestinal amyloidosis. 1.Lactulose is a synthetic sugar that cannot be digested and absorbed, directly into the colon after ingestion, the sugar in the colon >2g, lactulose is broken down by colonic bacterial strains or fermentation to produce hydrogen, CO2, methane, etc., there will be a phenomenon of hydrogen and methane concentration in the breath, from the oral to the time of the rise in the concentration of hydrogen and methane in the breath is the time the drug from the mouth to the cecum from the beginning of the large intestine is the run time, referred to as the Oral-blind passage time. 2. The oral-blind passage time roughly reflects the dynamics of the small intestine. If there is bacterial overgrowth in the small intestine, the oral lactulose will be broken down prematurely before it reaches the large intestine, resulting in two peaks of gas production. 3. Therefore more than 99% of the hydrogen in the exhaled breath is produced in the colon, and we can then confirm the presence of bacteria that should not be present in the small intestine by when hydrogen and methane are produced after taking lactulose. Of course this method has great limitations and is affected by a variety of factors such as whether or not you are taking antibiotics, the use of enemas, smoking, dietary habits, oral hygiene, etc. Therefore, it is best to consult with your doctor in advance when having the test done to correct the influencing factors and improve the accuracy of the test.