Glucose breath test (hydrogen breath test) at Wessex Hospital

Why might I need a glucose breath test?

You might be offered a glucose breath test if your doctor suspects small intestinal bacterial overgrowth (SIBO), a condition where bacteria that normally live in your large intestine grow in your small intestine instead, where they can interfere with digestion. It can cause symptoms such as:

• bloating and wind
• diarrhoea or a change in your bowel habits
• abdominal cramps or discomfort.

Different versions of the test, using other sugars such as lactose or fructose instead of glucose, are used to check for intolerance to those specific sugars.

What are the benefits of a glucose breath test?

The test is non-invasive and doesn't need any needles, so it avoids the risks of investigations such as an endoscopy or biopsy. It can help confirm whether bacterial overgrowth is causing your symptoms, so you can be offered the right treatment, usually a course of antibiotics.

Are there different types of breath test?

• Glucose breath test: used to check for small intestinal bacterial overgrowth (SIBO). Glucose is normally absorbed early in the small bowel, so if hydrogen or methane appears in your breath, this can suggest bacteria are digesting it somewhere they shouldn't be.
• Lactose breath test: checks for lactose intolerance, where your body struggles to break down the sugar found in milk and dairy products.
• Fructose breath test: checks for fructose malabsorption, where your body has difficulty absorbing the sugar found naturally in fruit.
• Lactulose breath test: sometimes used as an alternative way to test for SIBO, and can also give information about how quickly food moves through your small bowel.

You'll usually only be tested for the specific sugar named in your appointment letter, based on your symptoms.

How do I prepare for a glucose breath test?

• For about 4 weeks beforehand, avoid antibiotics if possible; if you're prescribed a course during this time, take it as normal and contact the department to rearrange your test.
• Avoid probiotics for several days to a few weeks beforehand; this varies between hospitals, so follow your specific instructions.
• For about a week beforehand, avoid laxatives, stool softeners, and medicines that affect how your gut moves, such as metoclopramide or domperidone.
• Avoid any test that needs bowel preparation, such as a colonoscopy, for some weeks before and after your breath test.
• The day before your test, eat only low-fibre foods, and avoid high-fibre foods, beans, pulses, and most fruit and vegetables.
• Fast, having nothing to eat or drink except water, for around 8 to 13 hours before your appointment; exact timings vary, so check your appointment letter.
• On the day, don't smoke, vape, or chew gum beforehand, and avoid alcohol-based mouthwash if you brush your teeth.
• You can usually take essential prescription medicines with a sip of water; tell the department if you're diabetic, as the sugary drink may affect your blood sugar levels and you may need to adjust your usual dose.

What happens during a glucose breath test?

1. A member of staff explains the test and checks your consent, answering any questions you have.
2. You blow into a bag or a handheld device to give a baseline breath sample, sometimes done twice to check your starting reading is low enough to continue.
3. You drink a sugary solution containing the specific sugar named in your appointment letter, such as glucose.
4. You give further breath samples at regular intervals, often every 15 to 30 minutes, for up to around 2 to 4 hours.
5. You're asked not to eat, drink, smoke, sleep, or exercise while you wait between samples, so it can help to bring a book or something else to pass the time.

The whole test can take anywhere from around 90 minutes to 4 hours, depending on which sugar is used and your hospital's protocol.

What happens after a glucose breath test?

You can usually go home or back to work straight away, and your ability to drive isn't affected. You can eat and drink normally again once the test is finished, and restart any medicines you paused beforehand.

Some hospitals will tell you a provisional result before you leave. A full written report is usually sent to the doctor who referred you, and sometimes to you and your GP too.

If bacterial overgrowth is confirmed, this is usually treated with a course of antibiotics. Most people's symptoms settle, though a few need a repeat course if symptoms come back.

What are the risks of a glucose breath test?

• Bloating, wind, diarrhoea, or a temporary worsening of your usual symptoms: possible during or shortly after the test, since you're drinking a sugar solution that can be hard for your gut to process if you have an underlying problem.
• Feeling short of breath: unlikely, since you're only asked to breathe at your normal rate when giving samples.

Some hospitals state there are no significant risks associated with this test, since it doesn't involve any needles, dyes or radiation.