Hydrogen Breath Tests
Bloating, flatulence, abdominal pain, and diarrhea are common complaints. Some of the patients are diagnosed as having IBS. Yet, high rate of the general population suffer from carbohydrate malabsorption that might respond to dietary change and specific treatments. Identification of these patients and adequate treatment might improve symptoms and their quality of life. Approximately 75% of the human population has a reduced ability to digest lactose after infancy. However, symptomatic malabsorption is seen in only a fraction of the population and is called lactose intolerance. Lactase deficiency can be a primary autosomal recessive condition or secondary to a disease process such as in celiac disease, gastroenteritis, and Crohn’s disease, leading to transient lactase deficiency and appearance of abdominal symptoms.
Fructose is a monosaccharide commonly found in fruits and as a sweetener. It is absorbed along the small bowel in a passive diffusion, facilitated by glucose transport protein 5 (GLUT5). Thus, fructose absorption is physiologically limited. In contrast to lactose, malabsorption of fructose tends to decrease with age.
The definition of SIBO (small intestinal bacterial overgrowth) depends on the concentration of bacteria in certain anatomical locations along the small bowel. Patients with SIBO may be clinically asymptomatic or may have symptoms that fit the diagnostic criteria of IBS. Presumed pathogenesis is mucosal injury, induced by bacteria or their toxins, or the presence of intraluminal bacteria causing malnutrition and vitamin deficiencies. In old age patients, motility disorders are probably the major cause of development of SIBO.
The diagnosis of the abovementioned conditions requires detailed medical history, dietary and lifestyle assessment, in some cases also blood and fecal tests, endoscopy and radiological imaging. Exclusion diets can be the first diagnostic modality for carbohydrate malabsorption. In patients suspected of having IBS, low short chain fermentable carbohydrates (low FODMAP) diet is considered the most successful exclusion diet.
Hydrogen and/or methane breath testing are useful, indirect, noninvasive measures to assess carbohydrate malabsorption in the gastrointestinal tract. In these tests, a measured amount of lactose or fructose are given to the patient. The unabsorbed carbohydrate is metabolized by the gastrointestinal microbiota producing hydrogen or methane which is absorbed into the bloodstream and expired via the lungs. Lactulose is used for SIBO diagnosis, as this carbohydrate is metabolized solely by the gut microbiota, a high hydrogen/methane reading of the test is diagnostic for SIBO. The tests have an excellent safety profile, but there appears to be huge individual inter- and intra-variability in the amount and the duration of gas production, that does not correlate with symptom profile or severity.
Treatment for lactose intolerance includes reduction of lactose intake. Tolerance may be induced by repeated lactose dosing due to adaptation of the intestinal flora. Compliance with a fructose-restricted diet may significantly improve symptoms of fructose intolerance, especially in a patient primarily diagnosed with IBS. The primary goal of therapy in SIBO is the treatment of any underlying disease or structural defect. Treatment of SIBO aims to modify the GI microbiota, thus many different antibiotic regimens have been advocated for use in SIBO. Recently, a locally active antibiotic—rifaximin—was used successfully in patients with SIBO. Pilot studies address the use of probiotics in SIBO. SIBO is a relapsing disease, especially when there are predisposing factors and may require repeat antibiotic use.
KeywordsCarbohydrate malabsorption Lactose intolerance Fructose intolerance SIBO IBS Hydrogen breath test Methane breath test
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