Fig. 1: Pattern of glucose hydrogen breath test in irritable bowel syndrome
patients with and without small intestinal bacterial overgrowth (SIBO)
Small intestinal bacterial overgrowth is caused by change in either intestinal motility or defense mechanism of the small bowel and results in reduced clearance of bacteria. The gold standard for the diagnosis of small intestinal bacterial overgrowth involves demonstrating the presence of >105 colony forming units/ml of jejunal fluid. However, this method is impractical, carries the risk of contamination (9) and the results of culture are not always representative. It is commonly believed that culture may give false negative results, especially where obligate anaerobes are concerned.(10) Because of this disadvantage, various breath tests have been developed. Non-invasive breath testing, measuring the production of H2 or methane or both after ingestion of non-fermentable carbohydrate such as glucose8 or lactulose(11) is commonly used to diagnose small intestinal bacterial overgrowth.
Glucose is readily absorbed in the proximal small bowel (jejunum) and in the absence of severe transit abnormalities rarely reaches the colon(12) making it an attractive substrate to detect small intestinal bacterial overgrowth The glucose hydrogen breath test is considered positive if there is a clearly recognisable hydrogen peak, exceeding 10 ppm.(8,13) Therefore, glucose hydrogen breath test has been used in the present study to detect small intestinal bacterial overgrowth.
In this study, we observed a high prevalence (11.1%) of small intestinal bacterial overgrowth in IBS patients when compared with controls (1%). In contrast to our findings, Pimentel et al in 200314 reported a very high prevalence of small intestinal bacterial overgrowth (78%) in IBS patients. They used lactulose as a substrate in their study. The positive breath test obtained using lactulose may have been due to the hydrogen production by colonic bacteria. Galatola et al,(7 )found that up to 29% of patients with irritable bowel syndrome without diarrhoea (faecal weight < 600 g/72 h) and 56% of those with diarrhoea of obscure origin had a positive C14-xylose test, suggesting small intestinal bacterial overgrowth. They concluded that although the C14-xylose test had a high diagnostic value in the setting of clinical research, it could not be used as a routine investigation tool.C14-xylose breath test has been proposed as a very sensitive and specific test for the diagnosis of bacterial overgrowth. However, till date, there is no general agreement on which is the preferred test for the diagnosis of small-intestinal bacterial overgrowth. In a recent study, Posserud et al assessed the prevalence of SIBO, by culture of small-bowel aspirate in 162 patients with IBS.15 SIBO was found in 4% of both patients and controls and the authors concluded that the data did not support an important role for SIBO according to commonly used clinical definitions, in IBS. However as the hypothesis suggesting SIBO as a component of IBS remains attractive, it has led to renewed scrutiny of tests employed to diagnose SIBO and its prevalence in the heterogenous population of irritable bowel syndrome.
To summarise, we have shown that there is a higher prevalence of small intestinal bacterial overgrowth in patients with irritable bowel syndrome from North India as compared to healthy controls.
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