Diagnostic Tests for SIBO 2018-04-14T19:21:20+00:00

Diagnostic Tests for SIBO

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Hydrogen Breath Test (HBT)

At IBS Clinics, we offer a range of tests for Small Intestinal Bacterial Overgrowth (SIBO).

The HBT is a simple, inexpensive and non-invasive test used to identify SIBO. It measures the hydrogen and methane gas produced by the bacterial fermentation of the sugars that the bacteria absorb. The gases produced diffuse into the blood, and then into the lungs, for expiration.

The test involves drinking a sugar solution, and giving breath samples at 20 minute intervals for 60 -180 minutes. The tests are inexpensive and can be done at the laboratory or at home.

Lactulose Breath Test (LBT)

The LBT also measures levels of hydrogen and methane and can diagnose overgrowth in the distal end of the small intestine (the portion closest to the colon), where it is thought to be most prevalent. However, the test is less sensitive than the glucose breath test.

Glucose Breath Test (GBT)

Glucose is usually absorbed within the top two feet of the small intestine; so if hydrogen and methane are found in this test it indicates an overgrowth in upper end of the small intestine, closest to the stomach.

This test is better at diagnosing bacterial overgrowth of the top portion of the small intestine but cannot identify an overgrowth further along the gut.


The breath test considered to be the gold standard for identifying SIBO uses Lactulose, a poorly absorbed sugar.

The lactulose solution is drunk and breath tested every 20 minutes for 3 hours. If bacteria are present in the small intestine they will metabolise the sugar and produce hydrogen, methane or both gases. The levels of these gases are tracked and if elevated in the first 2 hours of the test, the test is considered positive. The NHS often uses glucose as its preferred substrate for SIBO testing. Whilst glucose offers a slightly better specificity for the identification of SIBO than lactulose, in patients whose bacterial overgrowth is in the duodenum (top 3 feet of small intestine), its rapid absorption means that it is unable to identify bacterial overgrowth farther along the small intestine. In our experience, SIBO is more likely to be found in the distal end of the small intestine and therefore a lactulose solution produces more accurate results.

Lactose and Fructose Breath Tests

Lactose and Fructose intolerance can be tested in a very similar fashion.
Elevations in gases identify bacterial metabolism of unabsorbed lactose or fructose in the small intestine which indicates an inability to digest them.

Flatline SIBO Breath Test Result?

Increasingly, we have been seeing hydrogen breath tests with a curious flat line presentation. Experience and much research has shown that many people with SIBO-like symptoms and a “negative” breath test have a bacterial overgrowth of a bacterium that can re-metabolise the hydrogen produced by other gut flora and create hydrogen sulphide.

Hydrogen sulphide is not identified by the breath test machines used by laboratories. In these instances we tend to assume the existence of SIBO and proceed accordingly. Patients respond favourably to this approach. For the avoidance of doubt I have been able to source a urine based home test for hydrogen sulphide, which is extremely inexpensive and gives immediate results.

To find out more and learn how we can help you, please contact us