The hydrogen breath test (HBT) is a non-invasive diagnostic procedure used to measure the amount of hydrogen and, often, methane gas present in a person’s exhaled breath. This test helps medical professionals evaluate how the body digests certain sugars and carbohydrates. These gases are produced when unabsorbed sugars travel to the large intestine or encounter an overgrowth of bacteria in the small intestine, leading to fermentation. The gases are then absorbed into the bloodstream, transported to the lungs, and expelled through the breath, where they are quantified in parts per million (ppm).
Essential Preparation Before the Test
The accuracy of the hydrogen breath test depends on strict adherence to preparatory guidelines. Preparation aims to reduce the bacterial load and minimize fermentable material in the gut. Patients must follow a restricted, low-fermentable diet for at least 24 to 48 hours before the test. This diet limits high-fiber foods, whole grains, fruits, and vegetables, favoring simple options like plain steamed white rice, baked fish, or poultry.
A mandatory fasting period, usually lasting 8 to 12 hours, is also enforced. During this fast, only plain water is permitted; patients must abstain from everything else, including chewing gum, mints, or brushing their teeth shortly before the test. Certain medications must be discontinued well in advance, with antibiotics and probiotics often stopped for up to four weeks prior. Smoking and vigorous exercise are restricted on the day of the test, as these activities can skew the baseline readings.
Step-by-Step Procedure and Total Duration
The procedure begins with the collection of an initial, or baseline, breath sample upon arrival. The patient exhales into a collection device connected to an analyzer to establish the starting concentration of hydrogen and methane gases. A low baseline reading confirms the effectiveness of the pre-test fasting and dietary restrictions.
Following the baseline collection, the patient consumes a specific liquid solution containing a test substrate (such as lactulose, glucose, lactose, or fructose) mixed in water. The choice of substrate depends on the condition the doctor suspects (e.g., lactose for intolerance or lactulose for SIBO). The patient then remains at the facility while subsequent breath samples are collected at regular intervals.
These intervals are typically spaced every 15 to 30 minutes and continue for a total duration that usually spans two to three hours. This extended time is necessary to allow the ingested solution to travel through the stomach and small intestine, giving any bacteria present time to ferment the substrate and produce gas. The overall time commitment is substantial, ranging from 120 to 180 minutes, as the medical team monitors the gas levels for a rise over the course of digestion.
Conditions Identified by the Hydrogen Breath Test
The test diagnoses specific gastrointestinal disorders by identifying abnormal patterns of gas production after ingesting a sugar solution. A common application is detecting carbohydrate malabsorption, such as lactose or fructose intolerance. In these instances, the body lacks the necessary enzymes to break down the sugar, causing it to reach the colon undigested and be fermented by gut bacteria.
A significant rise in breath hydrogen, usually defined as an increase of 20 parts per million above the baseline, indicates a positive result for sugar malabsorption. The test is also a standard tool for diagnosing small intestinal bacterial overgrowth, or SIBO, where an excessive number of bacteria colonize the small intestine. For SIBO, an early peak in gas levels, often within the first 90 minutes, suggests that bacteria in the upper gut fermented the substrate before it could reach the large intestine.