The basis of the test is a failure to absorb the given sugar, which is then metabolized by bacteria that give off either hydrogen or methane.
If the level of hydrogen rises above 20 ppm (parts per million) over the lowest preceding value within the test period, the patient is typically diagnosed as a fructose malabsorber.
The patient is then given a small amount of pure lactose (typically 20 to 25 g), and then required to take readings every 15, 30 or 60 minutes for two to three hours.
If the level of hydrogen rises above 20 ppm (parts per million) over the lowest preceding value within the test period, the patient is typically diagnosed as a lactose malabsorber.
Lactulose is not absorbed by the digestive system and can help determine distal end bacterial overgrowth, which means the bacteria are lower in the small intestine.
The idea that a SIBO test should be several hours long and that distal overgrowth is important is not supported by the scientific literature.
Secondly, the consequences of SIBO are the result of competition between bacteria and the human host for ingested nutrients in the intestine.
The SIBO breath test typically uses a 10 gram oral dose of lactulose for detection of proximal bacterial overgrowth.
Since SIBO occurs in the proximal intestine, breath samples should be collected only within 1 hour after lactulose ingestion.
Diagnostic criteria of 20 ppm hydrogen and/or methane changes within 90 or 120 minutes will have higher positive rates of SIBO but this will reflect colonic activity not jejunal metabolism.
An increase of approximately 12 ppm or more in hydrogen and/or methane during the breath test could conclude bacterial overgrowth.