Complete ROSH Gastrointestinal Practice Exam 2025

The hydrogen breath test is commonly used to confirm lactose intolerance because it specifically measures the amount of hydrogen in the breath after the ingestion of lactose. When a person who is lactose intolerant consumes lactose, their body can't effectively digest it due to a deficiency of lactase, the enzyme necessary for lactose breakdown. As a result, the undigested lactose reaches the colon, where bacteria ferments it, producing hydrogen and other gases. The hydrogen is then absorbed into the bloodstream, carried to the lungs, and expelled in the breath. A significant increase in hydrogen levels after lactose ingestion indicates that lactose is not being properly digested, confirming lactose intolerance.

Other tests listed do not specifically evaluate lactose metabolism. For instance, anti-gliadin antibodies are used to detect celiac disease, the sweat test is used for cystic fibrosis, and the urea breath test is primarily used to identify Helicobacter pylori infection. Thus, these options are not relevant for assessing lactose intolerance.