What does the hydrogen breath test measure, and what does a positive result indicate?

The hydrogen breath test is a diagnostic tool primarily used to measure the production of hydrogen gas in the breath after the ingestion of a specific sugar substrate, typically lactose, fructose, or glucose. Bacteria present in the intestines can ferment these sugars, producing hydrogen as a byproduct.

When a patient consumes the sugar substrate, any undigested or unabsorbed sugars will reach the colon, where bacteria may ferment them, leading to the production of hydrogen. The test measures the amount of hydrogen in the breath at regular intervals.

A positive result in this test indicates the presence of bacterial overgrowth in the small intestine. Normally, the bacteria are primarily in the large intestine, and a significant amount of hydrogen production after ingesting these sugars suggests that there may be an abnormal amount of bacteria in the small intestine, often causing symptoms like bloating, diarrhea, or abdominal pain due to malabsorption.

This is an important diagnostic step as it can help identify conditions such as small intestinal bacterial overgrowth (SIBO), which requires specific treatment strategies differing from those for other gastrointestinal disorders.