Hydrogen breath tests (HBT) are non-invasive investigations frequently used in pediatric gastroenterology. The range of diseases that can be identified include carbohydrate intolerance, small intestinal bacterial overgrowth, and orocecal transit time. In the normal individual, gut bacteria are primarily located in the colon and the distal small intestine. When defective sugar absorption is present, unabsorbed carbohydrates make up the substrate for the saccharolitic flora of the colon. Short-chain fatty acids and gases (e.g. hydrogen [H2], methane [CH4]) are formed from the metabolism of this flora. Human cells do not produce H2 and CH4. The rationale of HBT is based on the concept that part of the gas produced by colonic bacterial fermentation diffuses into the blood and is excreted by breath, where it can be quantified easily by chromatography .
Breath testing is designed around the fact that all hydrogen in the breath results from fermentation of poorly absorbed carbohydrate in the intestinal tract (Figure 1). Interpretation is easier if breath hydrogen starts at zero – hence a diet low in fermentable carbohydrates is recommended the day before the test. Only one sugar can be tested each day, with an interval of at least 2 days between tests.
Patients were asked to fast from solids and liquids for a minimum of 8 hours (overnight) before the test and to have only small amounts of water; tests were conducted in the morning and patients fasted from midnight. In order to avoid false-positive and false-negative results, patients were asked to eat a low-fibre evening meal, not to have exercised in the morning of or during the test, and not to have taken antibiotics, probiotics, prokinetics, laxatives and/or solutions for colonic clearing within 4 weeks before the test. Good oral hygiene was also recommended.
The pretest diet is important to ensure low baseline breath hydrogen. The test solution is consumed after a baseline breath sample, followed by repeated breath samples over 3 hours. A rise in breath hydrogen (or methane) indicates malabsorption through fermentation of the test sugar.
All patients with functional gut symptoms undergoing breath tests should receive dietary advice, preferably by a diaetician. The tests do not determine whether dietary change is worthwhile – it only guides the dietician in designing the diet.