How is Small Intestinal Bacterial Overgrowth (SIBO) diagnosed?

Small intestine bacterial overgrowth (SIBO), also termed bacterial overgrowths, or small bowel bacterial overgrowth syndrome (SBBOS), is a disorder of excessive bacterial growth in the small intestine. Unlike the colon (or large bowel), which is rich with bacteria, the small bowel usually has fewer than 10,000 organisms per ml. A common misconception is that SIBO affects only a limited number of people, such as those with an anatomic abnormality of the upper gastrointestinal (GI) tract or those with a motility disorder. However, SIBO may be more prevalent than previously thought. Small bowel bacterial overgrowth syndrome is treated with an elemental diet or antibiotics, which may be given in cycles to prevent development of tolerance.

How is SIBO diagnosed?

The diagnosis of bacterial overgrowth can be made by physicians in various ways. Malabsorption can be detected by the D-xylose test. D-xylose is a monosaccharide, or simple sugar, that does not require enzymes for digestion prior to absorption. Its absorption requires an intact mucosa only. The D-xylose test involves having a patient drink a certain quantity of D-xylose, and measuring levels in the urine and blood. Little or no D-xylose in the urine and blood indicates issues with absorption in the small intestine.

Another common way to diagnose SIBO is by undergoing a Hydrogen breath test. This is a test for bacterial overgrowth using glucose. Glucose is a sugar that will be broken down by bacteria (if present) in the small bowel. The breakdown of glucose releases hydrogen or methane gas. The breath sample will be analyzed for hydrogen or methane content to determine if you are able to properly break down the glucose or if you have bacterial overgrowth. If you are not able to break down the glucose, then your breath test is positive and you have SIBO.

Small intestine aspirate and fluid culture is currently the gold standard test for bacterial overgrowth. To obtain the fluid sample, doctors pass a long, flexible tube (endoscope) down the patient’s throat and through the upper digestive tract to the small intestine. A sample of intestinal fluid is withdrawn and then tested in a laboratory for the growth of bacteria.

What are the symptoms of SIBO?

Chronic diarrhea, bloating, abdominal swelling, gas and belching, abdominal pain or fullness after eating, alteration of bowel habits (constipation, diarrhea or alternating with both)

What is the treatment?

Bacterial overgrowth is usually treated with a course of antibiotics although some experts recommend probiotics as first line therapy with antibiotics being reserved as a second line treatment for more severe cases. A course of one week of antibiotics is usually sufficient to treat the condition. However, if the condition recurs, antibiotics can be given in a cyclical fashion in order to prevent tolerance. For example, antibiotics may be given for a week, followed by three weeks off antibiotics, followed by another week of treatment. Alternatively, the choice of antibiotic used can be cycled.

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