Unfortunately there is no perfect test. The small intestine (SI) is a hard place to get to. If we want to see or sample the SI, endoscopy only reaches into the top portion, and colonoscopy only reaches into the end portion. The middle portion, which is substantial (about 17 feet) is not accessible, other than by surgery. And stool testing predominantly reflects the large intestine (LI). Luckily, there is a non-invasive test which is commonly used in SIBO research; the Hydrogen Breath Tes
Hydrogen Breath Test
A hydrogen breath test can be used to diagnose several conditions: H pylori infection, carbohydrate malabsorption (ex. lactose) and SIBO.
SIBO Breath Test
Breath testing measures the hydrogen (H) & methane (M) gas produced by bacteria in the SI that has diffused into the blood, then lungs, for expiration. H & M are gases produced by bacteria, not by humans. The gas is graphed over the SI transit time of 2 or 3 hours & compared to baseline. Patients drink a sugar solution of glucose or lactulose after a 1 or 2 day preparatory diet. The diet removes much of the food that would feed the bacteria, allowing for a clear reaction to the sugar drink.
Two types of tests may be used: Lactulose or Glucose.
Lactulose Breath Test (LBT)
Humans can’t digest or absorb lactulose. Only bacteria have the proper enzymes to do this. After they consume lactulose, they make gas. If there is an overgrowth, this will be reflected in the levels of H and/or M.
The advantage to this test is that it can diagnose overgrowth in the distal end of the SI, thought to be more common. The disadvantage is that it cannot diagnose bacterial overgrowth as well as the Glucose Breath Test (GBT).
Glucose Breath Test (GBT)
Both humans and bacteria absorb glucose. Glucose is absorbed within the first three feet of the SI, therefore if the bacterial gases of H and/or M are produced during this test, it reflects an overgrowth in the proximal/upper end of the SI (within the first two feet).
The advantage to this test is that it successfully and accurately diagnoses proximal overgrowth. The disadvantage is that it cannot diagnose distal overgrowth, occurring in the latter 17 feet of the SI, which is thought to be more common.