Intestinal Gas (Belching, Bloating, Flatulence) (cont.)
William C. Shiel Jr., MD, FACP, FACR
William C. Shiel Jr., MD, FACP, FACR
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
In this Article
How are belching, bloating/distention, and flatulence evaluated?
A patient's medical history is important because it directs the evaluation.
Simple abdominal X-rays
Simple X-rays of the abdomen, particularly if they are taken during an episode of bloating or distention, can often confirm air as the cause of the distention since large amounts of air can be seen easily within the stomach and intestine. Moreover, the cause of the problem may be suggested by noting where the gas has accumulated. For example, if the air is in the stomach, emptying of the stomach is likely to be the problem.
Small intestinal X-rays
X-rays of the small intestine, in which barium is used to fill and outline the small intestine, are particularly useful for determining if there is an obstruction of the small intestine.
Gastric emptying studies
These studies measure the ability of the stomach to empty its contents. For gastric emptying studies, a test meal that is labeled with a radioactive substance is eaten and a Geiger counter-like device is placed over the abdomen to measure how rapidly the test meal empties from the stomach. A delay in emptying of the radioactivity from the stomach can be caused by any condition that reduces emptying of the stomach (for example, pyloric stenosis, gastroparesis).
Ultrasound, CT scan, and MRI
Imaging studies, including ultrasound examination, computerized tomography (CT), and magnetic resonance imaging (MRI), are particularly useful in defining the cause of distention that is due to enlargement of the abdominal organs, abdominal fluid, and tumor.
Maldigestion and malabsorption tests
Two types of tests are used to diagnose maldigestion and malabsorption; general tests and specific tests.
The best general test is a 72 hour collection of stool that measures fat in the stool; if maldigestion and/or malabsorption exist because of pancreatic insufficiency or diseases of the lining of the small intestine for example, celiac disease), the amount of fat in the stool will increase.
Specific tests can be done for maldigestion of individual sugars that are commonly maldigested, including lactose (the sugar in milk) and sorbitol (a sweetener in low calorie foods). The specific tests require ingestion of the sugars followed by hydrogen/methane breath testing. (See below.) The sugar fructose, a commonly used sweetener, like lactose and sorbitol, also may cause abdominal bloating/distention and flatulence. However, the problem that can occur with fructose is different from that with lactose or sorbitol. Thus, as already described, lactose and sorbitol may be poorly digested by the pancreatic enzymes and small intestine. On the other hand, fructose may be digested normally but may pass so rapidly through the small intestine that there is not enough time for digestion and absorption to take place.
Hydrogen/methane breath tests
The most convenient way to test for bacterial overgrowth of the small intestine is hydrogen/methane breath testing. Normally, the gas produced by the bacteria of the colon is composed of hydrogen and/or methane. For hydrogen/methane breath testing, a non-digestible sugar, lactulose, is consumed. At regular intervals following ingestion, samples of breath are taken for analysis. When the lactulose reaches the colon, the bacteria form hydrogen and/or methane. Some of the hydrogen or methane is absorbed into the blood and eliminated in the breath where it can be measured in the samples of breath.
In normal individuals, there is one peak of hydrogen or methane when the lactulose enters the colon. In individuals who have bacterial overgrowth, there are two peaks of hydrogen or methane. The first occurs when the lactulose passes and is exposed to the bacteria in the small intestine. The second occurs when the lactulose enters the colon and is exposed to the colonic bacteria. Hydrogen breath testing for overgrowth also may be done utilizing lactose, glucose, sorbitol, or fructose as the test sugar.
Reviewed by William C. Shiel Jr., MD, FACP, FACR on 4/18/2012
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