Paediatric Hydrogen Breath Test

Patient Leaflets Team

  • Reference Number: HEY-747/2016
  • Departments: Paediatrics
  • Last Updated: 1 March 2016


This leaflet has been produced to give you general information about your child’s forthcoming hydrogen breath test.  Most of your questions should be answered by this leaflet.  It is not intended to replace the discussion between you, your child and their doctor, but may act as a starting point for discussion.  If after reading it you have any concerns or require further explanation, please discuss this with a member of the healthcare team caring for your child.

What is a hydrogen breath test?

A hydrogen breath test is a non-invasive and safe investigative test used to look into intestinal disorders.  Your child will be given a test solution to drink after fasting (not eating) overnight.  The concentration of hydrogen (measured in parts per million) in the breath is then measured using a breath test machine.  If the breath sample contains a large amount of hydrogen (more than 20 parts per million above your baseline) it will be deemed a positive test. The baseline is the amount of hydrogen that is present in the breath before drinking the test solution.

Why does your child need a hydrogen breath test?

Due to your child’s symptoms your doctor has decided that they should be tested for one of three reasons (described below):

 To Test for Lactose Intolerance

Lactose is a natural sugar found in milk. Lactose intolerance is the inability of the body to breakdown lactose.  The problem is usually caused by a lack of a substance known as lactase. Lactase is an enzyme (a protein that causes a chemical reaction to occur) that is normally produced in the small intestine.

If your child’s body produces very little or no lactase it will be unable to break down the lactose in their system. The unabsorbed lactose passes through the stomach and into the large bowel.  Bacteria in the large bowel react to lactose producing fatty acids such as acetate and gases, examples of which are hydrogen and methane.   This can cause symptoms such as stomach bloating and flatulence (wind).  By measuring the hydrogen in your child’s breath over a period of time (after a drink of lactose) we can see if lactose intolerance may be the cause of their symptoms.

To Test for Small Bowel Bacterial Overgrowth

It is normal for bacteria to live in the large intestine as they aid digestion. However, the small intestine does not usually contain bacteria.  Sometimes bacteria can grow in the small intestine and interfere with the digestion of food; this is a condition known as ‘small bowel bacterial overgrowth’.

When bacteria digest sugar they produce hydrogen, which escapes from the gut via the lungs.  By measuring the hydrogen in your child’s breath over a period of time (after a drink of glucose) we can see if small bowel bacterial overgrowth may be the cause of their symptoms.

To measure Oro-Caecal Transit Time

Oro-caecal transit time is the time it takes for food/liquid to leave the mouth and reach the caecum at the start of the large intestine. This test will tell us if your child’s oro-caecal transit time is normal, fast or delayed.

Humans cannot digest lactulose and therefore it passes to the colon unchanged where it is fermented (reacted on) by bacteria to produce hydrogen that is excreted in the breath.  Therefore, by measuring the hydrogen in your child’s breath over a period of time (after a drink of lactulose) there is always a rise in breath hydrogen, which reflects delivery of lactulose to the caecum. This is taken as the oral-caecal transit time.

Can there be any complications or risks?

The test substance is a sugar solution i.e. lactose, glucose or lactulose.  The test in some cases (although rare) has been known to cause mild diarrhoea.

How do I prepare my child for a hydrogen breath test?

It is necessary for your child to have nothing to eat from 6pm the night before the test. Water is allowed until midnight the night before the test. Please follow the diet sheet below for your child’s meals the day before the test. If your child is diabetic, please telephone the department for advice before the study.

 6 weeks before the appointment:

If your child has to take antibiotics within 6 weeks of the appointment please contact us to re-book the test. If you are not sure which medication you should take please contact the department to check.

5 days before the appointment:

Please ensure that your child does not take:

Prepulsid (Cisapride), Domperidone (Motilium), Metoclopramide (Maxolon), Movicol, Picolax, Lactulose or any laxative.

On the day of the test your child is not allowed to smoke.

What will happen?

You should go to the Children’s Outpatients Department, which is situated in the Women and Children’s Hospital at Hull Royal Infirmary.

When you have informed the receptionist that you have arrived, a member of staff from the Department of GI Physiology come and explain the hydrogen breath test to you.  The test is very easily performed.  It requires your child to breathe down a mouthpiece into a hand held machine that measures hydrogen.  Providing your child has fasted correctly, the first reading should be very low.   If this reading is excessively high, we may have to abort the test and ask you to return in a few hours or rebook the test for another day.

Your child will drink the test solution (either lactose, glucose or lactulose) and will then be asked to breathe into the machine at regular intervals for up to 4 hours (younger children can use a special face mask to collect the sample of breath).  After the test has finished your child may go back to school or home.

What happens afterwards?

The consultant in charge of your child’s care will be informed of the result and they will decide what to do next. It is reasonable to expect to hear from them within 4 weeks of the test date. 

Should you require further advice on the issues contained in this leaflet, please do not hesitate to contact the

GI Physiology Department on: Telephone (01482) 622155

Menu for the day prior to Hydrogen Breath testing

Please telephone the department for advice if your child is diabetic on telephone number (01482) 622155.


Rice Krispies or supermarket brand equivalent with milk (Not with coco)


Eggs (scrambled/poached/fried) Bacon

Toasted white bread with butter (white bread only not brown)


Chicken or fish (no batter / breadcrumbs)

Boiled potatoes, freshly mashed potatoes or chips (without skins)

Pudding can be any of the following:

Small portion of ice-cream, sugar free jelly, sugar free custard, natural plain yoghurt

Evening meal:

Cheese omelette (no vegetables)


Eggs (scrambled/poached/fried)

Toasted white bread with butter (white bread only not brown)


Ham or cheese sandwich – white bread with butter (white bread only not brown)


Rich tea biscuits

(No fruit, vegetables or wholegrain products)


Plain water/sugar free fruit squash

The order of breakfast lunch and evening meal can be altered if required.

General Advice and Consent

Most of your questions should have been answered by this leaflet, but remember that this is only a starting point for discussion with the healthcare team.

Consent to treatment

Before any doctor, nurse or therapist examines or treats your child, they must seek your consent or permission. In order to make a decision, you need to have information from health professionals about the treatment or investigation which is being offered to your child. You should always ask them more questions if you do not understand or if you want more information.

The information you receive should be about your child’s condition, the alternatives available for your child, and whether it carries risks as well as the benefits. What is important is that your consent is genuine or valid. That means:

  • you must be able to give your consent
  • you must be given enough information to enable you to make a decision
  • you must be acting under your own free will and not under the strong influence of another person

Information about your child

We collect and use your child’s information to provide your child with care and treatment. As part of your child’s care, information about your child will be shared between members of a healthcare team, some of whom you may not meet. Your child’s information may also be used to help train staff, to check the quality of our care, to manage and plan the health service, and to help with research. Wherever possible we use anonymous data.

We may pass on relevant information to other health organisations that provide your child with care. All information is treated as strictly confidential and is not given to anyone who does not need it. If you have any concerns please ask your child’s doctor, or the person caring for your child.

Under the General Data Protection Regulation and the Data Protection Act 2018 we are responsible for maintaining the confidentiality of any information we hold about your child. For further information visit the following page: Confidential Information about You.

If you need information about your child’s (or a child you care for) health and wellbeing and their care and treatment in a different format, such as large print, braille or audio, due to disability, impairment or sensory loss, please advise a member of staff and this can be arranged.

QR code to open leaflet