![]() ![]() 22, 25, 26, 27 False positive results may also be due to the oral bacterial flora and if the subject has failed to adhere to a low fibre diet the day before the test.Īlmost all carbohydrates from the diet are large polysaccharides or disaccharides. ![]() 18, 19, 20 Several other potential sources of error exist, such as carbohydrate malabsorption in chronic pancreatitis and coeliac disease, with false positive tests for SIBO due to colonic fermentation and gas production, 20, 21, 22, 23 and gastrointestinal motor disorders, where delayed gastric emptying may cause false negative tests 24 and rapid transit through the small bowel will produce false positive breath tests. However, a considerable proportion of non‐hydrogen producing bacteria, which can yield false negative results, has been observed in some 12, 16, 17 but not all studies. The hydrogen breath test depends on the presence of hydrogen producing bacteria. “Hydrogen breath tests are based on the fact that there is no source for hydrogen gas in humans other than bacterial metabolism of carbohydrates” ![]() 15įigure 1 Schematic drawing showing the principles behind breath tests. 11 Glucose 12, 13 or lactulose 14 are the most commonly used substrates for diagnosis of SIBO whereas the different sugars tested for carbohydrates malabsorption are given to detect these disorders. Smoking raises and exercise lowers hydrogen concentrations and is therefore not allowed during the test. The different tests are performed in the fasting state after at least one day of a low fibre diet. When exposed to bacteria in the bowel, the substrate will be metabolised to hydrogen, which is quickly absorbed, expired, and possible to measure in expired air (fig 1 1). When defective sugar absorption is present, unabsorbed sugars are available in the colon for bacterial fermentation, and in the case of SIBO the bacterial population migrates proximally in the small intestine gaining access to the sugars. 10 For these tests different carbohydrates are administered orally and the concentration of hydrogen is measured in expired air. Hydrogen breath tests are based on the fact that there is no source for hydrogen gas in humans other than bacterial metabolism of carbohydrates. In this article, we will review the literature on the use of hydrogen breath tests to detect carbohydrate malabsorption and SIBO, and highlight the controversies and inconsistencies in the interpretation of these tests, especially regarding the relevance of fructose malabsorption and SIBO in patients with functional gastrointestinal disorders. 8, 9 However, these tests are indirect, with several drawbacks and pitfalls. 4 In the search for possible pathophysiological factors of functional gastrointestinal disorders, several authors have used different hydrogen breath tests in recent years to detect various abnormalities, such as carbohydrate malabsorption 5, 6, 7 and small intestinal bacterial overgrowth (SIBO). 2, 3 The pathophysiology behind these disorders is still incompletely known. 1 Many of these symptoms are clustered together forming the functional gastrointestinal disorders, as defined by the Rome II criteria. Within the field of gastroenterology, the majority of symptoms cannot be explained by structural abnormalities detected on routine investigations. ![]()
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