Hydrogen Breath Test

The hydrogen breath test is a non-invasive test used to diagnose digestive disorders such as small intestinal bacterial overgrowth (SIBO) and lactose intolerance.

This tests measures gases in your breath after ingestion of a sugar solution. This provides understanding on how your gut is digesting and absorbing certain sugars.

How does the test work?

As the food we eat gets digested, hydrogen and methane are produced by bacteria in the gut. These gases then diffuse out of the bloodstream and move into the lungs where they are exhaled.

Higher-than-expected levels may suggest:

• Small intestinal bacterial overgrowth (SIBO): When excessive bacteria are present in the small intestine
• Carbohydrate intolerance (such as lactose intolerance): When certain sugars are not well absorbed and undergo fermentation by gut bacteria, leading to excessive gas production and abdominal symptoms.

The test is usually performed to assess one specific condition at a time. The type of sugar solution used will depend on the condition you are being evaluated for.

Why is this test done?

This test may be recommended if you have symptoms such as:

• Abdominal bloating
• Abdominal pain or discomfort
• Diarrhoea

The results will help to determine if SIBO or carbohydrate intolerance is contributing to your symptoms and guide further management.

What to expect before the test?

Certain foods, medications, and supplements can affect the accuracy of the test results

Before the test:

• You will be asked to follow a special diet for a short period
• Some medications (such as antibiotics, laxatives, probiotics, or fibre supplements) may need to be stopped if possible

You will need to fast before the test. You will be given specific preparation instructions closer to your test date.

What to expect during and after the test?

During the test:

• A baseline breath sample is collected by asking you to blow into the breath-testing device
• You will then drink a sugar solution
• Further breath samples are collected at regular intervals for up to 3 hours
• You may be asked to record any symptoms (such as bloating, pain, or diarrhoea) that occur during the test

This is a day procedure; you will be allowed home on the same day. You will also be able to resume your normal activities and diet once the test is complete.

Frequently Asked Questions

Are there any risks associated with the hydrogen breath test?

The hydrogen breath test is generally safe and well tolerated. The collection of breath samples does not carry any risk.

However, drinking the sugar solution may cause temporary abdominal symptoms, such as bloating, gas, abdominal discomfort, or diarrhoea.

Serious complications are not expected.

How long does the test take?

The test usually takes up to 3 hours, as breath samples are collected at regular intervals after you drink the sugar solution. You will not be required to stay in hospital overnight.