This test requires you to make some dietary changes, including fasting (avoiding eating and drinking) in the days leading up to the test.

Read this guidance now. Make a note of essential dietary changes. If you do not follow this guidance, we may have to cancel your test.

About a lactulose hydrogen breath test

This is a test to investigate bowel symptoms such as diarrhoea or abdominal (tummy) discomfort.

This test is a simple and useful way of determining if you have small bowel bacterial overgrowth (an increase in bacteria). This small bowel bacterial overgrowth may be causing your symptoms.

About lactulose

In this test, we give you lactulose to drink. We use lactulose (a sweet syrup) because it is a synthetic, non-absorbable sugar that passes through your entire small intestine.

When small bowel bacteria digest sugar they produce hydrogen, which escapes via your lungs when you breath out.

By measuring the hydrogen in your breath after you drink lactulose, we can see if you have an overgrowth of bacteria in your small bowel.

Alternatives to the test

We can use a trial of antibiotics to determine whether you have small bowel bacterial overgrowth. However, using antibiotics can lead to bacterial resistance (whereby bacteria learn to resist drug treatment). For this reason, we consider the breath test to be  a better option.

Side effects

Breath testing is safe. The only likely side effect is the temporary worsening of some of the symptoms that have caused us to give you this test.

Important

The test takes up to 4 hours to complete.

We recommend you bring with you something to read during the test (for example a book, magazine, or device with pre-loaded material).

Preparing for your test

Follow this guidance as you prepare for your test.

During the 4 weeks before

For 4 weeks before your test

Do not take any antibiotics.

Do not take any probiotics (capsules, powders or liquids.)

Do not eat yogurt.

During the 2 weeks before

For 2 weeks before your test Do not undergo any imaging of your small bowel.

During the week before

For 7 days before your test

Do not take any laxatives or medicines to soften your stools (poo).  Do not take any lactulose.

Do not undergo any test that requires cleansing of the bowel. This includes colonoscopy, barium enema or colonic irrigation.

During the days and hours before

For 48 hours before your test

Do not eat any of the following:

  • onions or garlic
  • pulses such as peas, beans and lentils
  • root vegetables such as potatoes, carrots and parsnips
  • fruit.
For 24 hours before your test

Only consume the following foods and drinks:

  • plain white bread
  • plain white rice
  • baked or boiled chicken or fish
  • regular black tea or coffee
  • salt to flavour food only.

Avoid all other foods and drinks.

  • Do not eat butter or margarine.
  • Do not drink soda or cola drinks.
For 12 hours before your test

Do not eat anything.

Only drink water.

For example if your test is at 9am, you must stop eating (and only drink water) from 9pm the night before.

  • You can take your prescription medicines as normal.
  • Do not smoke, chew gum or eat breath mints or sweets.

On the day of the test

 On the day of your test, you must not eat or drink anything (see Medicines below).

  • Do not use denture fixatives or adhesives.
  • 2 hours before the test: brush your teeth thoroughly. 

Medicines

On the day of the test you can take your usual medicines with a small amount of water.

If you are diabetic and need to take insulin or diabetic tablets, ask your referring doctor (GP or hospital) if you should change or skip your morning dose. Diabetic tablets are not normally taken on the morning of the test, until you restart eating and drinking immediately after the test.

During your test

  • You will need to remain sitting or standing.
  • You must not sleep or exercise while the test is underway.

You can expect the following during the test.

  • We will ask you to rinse your mouth out with an anti-bacterial mouthwash.
  • We will ask you to blow into the hydrogen breath analyser before you drink the lactulose. This will give us a baseline reading.
  • We will ask you to drink a lactulose solution.
  • We will ask you to breathe into the analyser every 20 minutes. You must do this for the next 2 to 3 hours. This will allow us to see if the level of hydrogen changes.
  • If there is bacterial overgrowth in your small intestine, the lactulose you drink will cause two separate peaks of hydrogen production. These are:
    • an early peak caused by the abnormal bacteria in your small intestine
    • a later peak caused by the normal bacteria of your large bowel.

After your test

  • You can eat and drink immediately after completing your test.
  • You can drive yourself home after the test.

Results

We will send your results to the Kingston Hospital consultant who is in charge of your small bowel investigation. They will interpret the results and send their findings to your referring doctor (GP or hospital).

Contact information

Endoscopy nurses advice line
2pm to 4pm
 

Gastroenterology bookings team (to reschedule or cancel appointments)
9am to 5pm (email: khn-tr.gastro@nhs.net)

Telephone:

Endoscopy nurses advice line: 020 8934 6614

Gastroenterology bookings team: 020 8934 2099, option 1 (or email)