Diagnosis

In order to diagnose small intestinal bacterial overgrowth (SIBO), you may have tests to check for bacterial overgrowth in your small intestine, poor fat absorption, or other problems that may be causing or contributing to your symptoms. Common tests include:

• Breath testing. This type of noninvasive test measures the amount of hydrogen or methane that you breathe out after drinking a mixture of glucose and water. A rapid rise in exhaled hydrogen or methane may indicate bacterial overgrowth in your small intestine. Although widely available, breath testing is less specific than other types of tests for diagnosing bacterial overgrowth.
• Small intestine aspirate and fluid culture. This is currently the gold standard test for bacterial overgrowth. To obtain the fluid sample, doctors pass a long, flexible tube (endoscope) down your throat and through your upper digestive tract to your small intestine. A sample of intestinal fluid is withdrawn and then tested in a laboratory for the growth of bacteria.

In addition to these tests, your doctor may recommend blood testing to look for vitamin deficiency or a stool evaluation to test for fat malabsorption. In some cases, your doctor may recommend imaging tests, such as X-rays, computerized tomography (CT) scanning or magnetic resonance imaging (MRI) to look for structural abnormalities of the intestine.