Small intestinal bacterial overgrowth can be difficult to diagnose, but making the diagnosis always starts with symptoms and a suspicion that SIBO is present based on those symptoms. Clinically significant SIBO never occurs without symptoms as noted in the previous articles on this site, so suffice it here to say that SIBO needs to be considered in all cases of bloating, abdominal discomfort, diarrhea, motility problems, and malabsorption of nutrients. Risk factors for SIBO are almost always present (see prior articles on this topic). Physical examination may help in severe cases but many times the findings are non-specific. The “gold standard” way to diagnose SIBO is by doing an endoscopic procedure during which fluid is collected out of the jejunum (a part of the small intestine) and then measuring the amount of bacteria present in the sample. Not only is this expensive and prone to lab error, but who wants to be sedated and invaded if there’s an alternative?
Fortunately, there is another way to diagnose SIBO, but remember, there’s no single perfect method. They all have their drawbacks. Nonetheless, hydrogen and methane breath tests are currently the most convenient and most widely used diagnostic methods and here’s how it works: Normally, the only source of hydrogen and methane in the body is from carbohydrate fermentation by bacteria in the LARGE intestine (a.k.a. the colon). However when colon bacteria colonize the small intestine, as in SIBO, fermentation of carbohydrates in the small intestine produces a significant amount of hydrogen and methane much earlier in the course of travel through the gastrointestinal tract. No matter where these gases are produced, about 20% of it is absorbed through the lining of the intestine and then exhaled in the breath. These exhaled gases can be measured in breath samples collected about every 15-20 minutes over a 3 hour period. So since it an average of 90 minutes for intestinal contents to travel through the small intestine, elevations of hydrogen or methane gas during this time may indicate small intestinal bacterial overgrowth.
Although breath testing is relatively low cost and simple, it’s accuracy is not great, ranging from 55-72% in reported studies. That means that there are a fair number of tests that result in either false positive or false negative results. Therefore if the breath test is inconclusive and other serious diagnoses have been ruled out, many clinicians will go ahead and treat the patient for symptoms that are consistent with SIBO.
There are a few other tests, such as urine organic acids and some serum tests, that have been proposed in the evaluation of SIBO but, at this time, none of these alone have the diagnostic accuracy that is needed for the diagnosis of SIBO. So be wary if you see a practitioner who suggests using urine or blood tests as the sole means for diagnosis.
Let me leave you with this encouragement: If you’re struggling with gastrointestinal issues that sound like SIBO or might be related to SIBO (bloating, flatulence, abdominal discomfort/cramping, diarrhea, constipation, etc.), get evaluated by a physician who is experienced in the diagnosis and treatment of this syndrome. It may make all the difference between continuing to suffer without any answers or finally finding a reason for your gut problem and getting healthy again.