A<unk>  (or<unk>  is used as a diagnostic tool for small intestine bacterial overgrowth and carbohydrate malabsorption, such as lactose, fructose, and sorbitol malabsorption. The test is simple, non-invasive, and is performed after a short period of fasting (typically 8–12 hours).<unk> s are based on the fact that there is no source for<unk>  gas in humans other than bacterial metabolism of carbohydrates. Even though the test is normally known as a<unk> "<unk>  test, some physicians may also test for methane in addition to<unk> . Many studies have shown that some patients (approximately 35% or more) do not produce<unk>  but actually produce methane. Some patients produce a combination of the two gases. Other patients, who are known as "non-responders", don't produce any gas; it has not yet been determined whether they may actually produce another gas. In addition to<unk>  and methane, some facilities also utilize carbon dioxide (CO2) in the patient's<unk>  to determine if the<unk>  samples that are being analyzed are contaminated (either with room air or bronchial dead space air). Physicians have expressed concern at the improper use and widespread overdiagnoses related to interpretation of these tests.
Hydrogen breath test
Urea breath test
Erythromycin breath test
Gluten challenge test
Capsule endoscopy
Sweat test
Fecal pH test
Salicylate testing