SIBO Breath Test: What to Expect

A SIBO breath test screens for small intestinal bacterial overgrowth by measuring hydrogen and methane gases in your breath after you drink a test solution. If bacteria in the small intestine ferment the solution, the gases they produce appear in your breath in measurable patterns over the following hours.

This is the most preparation-heavy at-home test, and the prep is where accuracy is won or lost. Kits typically prescribe a restricted prep diet for the day before — limiting fermentable foods so baseline gas levels are low — followed by an overnight fast of roughly twelve hours where only water is allowed. Kits commonly also advise avoiding smoking and vigorous exercise near the test, and your practitioner may advise on timing relative to antibiotics or other products.

You collect a baseline breath sample first, then drink the provided test solution — lactulose or glucose, depending on the kit. From there you collect breath samples at fixed intervals, commonly every 15 to 20 minutes for two to three hours, using the kit's tubes and following its schedule exactly. Label everything as you go, stay seated and relaxed between samples, and don't eat until the test is complete.