Evaluation of small bowel bacterial overgrowth

Small bowel bacterial overgrowth historically has been associated with malabsorption syndrome attributed to deconjugation of bile acids in the upper small intestine. Recent reports raise the possibility that bacterial overgrowth may be a cause of watery diarrhea or irritable bowel syndrome. Quantitative culture of jejunal contents has been the gold standard for diagnosis, but a variety of indirect tests have been developed (and mostly discarded) over the years in an attempt to facilitate the diagnosis of small bowel bacterial overgrowth. These include breath tests and biochemical tests based on bacterial metabolism of various substrates. Problems with these indirect tests include rapid transit, which may cause substrate to reach the luxuriant bacterial flora in the colon, producing false positives and vagaries of the tests themselves, which may produce falsely negative results. The perfect test for small bowel bacterial overgrowth is yet to be devised.