Hydrogen Breath Test

Patient Leaflets Team

  • Reference Number: HEY-092/2019
  • Departments: GI Physiology
  • Last Updated: 18 October 2019


This leaflet has been produced to give you general information. Most of your questions should be answered by this leaflet. It is not intended to replace the discussion between you and the healthcare team, 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.

What is a Hydrogen Breath Test

A hydrogen breath test is a non-invasive and safe test used to investigate intestinal disorders. You will be given a test solution to drink after you have fasted (not eaten) overnight. The concentration of hydrogen in your breath is then measured using a hydrogen breath test machine.

Why do I need a Hydrogen Breath Test

A hydrogen breath test provides information about the digestion of certain sugars or carbohydrates. This will help determine if you are intolerant to, or cannot digest, certain sugars. One example is lactose (milk sugar) intolerance, a disorder in which people develop symptoms after eating dairy products or foods which contain lactose.

The test is also used for detecting abnormal growth of bacteria within the small intestine. It is normal for bacteria to be found in your large intestine as they aid digestion. However, sometimes bacteria can grow in the small intestine and interfere with the digestion of food; this is a condition known as Small Intestinal Bacterial Overgrowth (SIBO). We usually administer lactulose (a non-digestible sugar) for this test. Bacterial overgrowth can cause a variety of symptoms including nausea, diarrhoea, bloating, gas, and abdominal cramps.

Can there be any complications or risks?

The test substance is a sugar solution i.e. lactose, glucose or lactulose. The test solution in some cases (although rare) could cause loose stools.

How do I prepare for the Hydrogen Breath Test?

Please read this information leaflet. Share the information it contains with your partner and family (if you wish) so that they can be of help and support.

Four (4) weeks before your test:

You should not take any antibiotics. If you have to take antibiotics please call the department to re-book the test.

One (1) week before your test:

You should not undergo any test that requires cleansing of the bowel such as colonoscopy, barium enema or colonic irrigation.  Do not take any laxatives, stool softeners, stool bulking agents or any medication used to treat constipation.

You should not take any probiotic yoghurts/probiotic supplements.

The day before your test:           

Please follow the menu below for your meals the day before the test.  If you are diabetic please telephone the department for advice on (01482) 624036.

Please note: Dairy products of any kind (including butter/spreads) are not allowed. The order of the meals may be changed.  It is essential that you do not eat or drink anything other than the foods and drinks listed below.

Do not eat anything from 6pm the day before the test. Drinking water is allowed until the start of the test.

The day of your test:

You should not eat anything in the morning, a little water is allowed.

Do not eat, drink, chew gum, smoke cigarettes (inc. E-cigarettes), eat breath mints or other sweets before or during the test.

Do not sleep or exercise while the test is being carried out as this can interfere with the result.

What will happen?

Please attend the department of GI physiology, which is situated adjacent to Ward 14 (1st floor).  This is located via Entrance 2, Main reception, Castle Hill Hospital.

 A member of staff from the GI Physiology Department will explain the hydrogen breath test to you. This is to ensure that you understand the test and its implications. The test is very easily performed. It requires you to breathe down a mouthpiece into a hand held machine that measures hydrogen. The breath samples are collected whilst you are blowing at your normal rate, therefore this should not make you short of breath.

Providing you have fasted correctly and have not smoked, the first reading should be very low. If this reading is excessively high, we may have to ask you to return in a few hours, or re-book the test for another day. You will drink the initial test solution (lactulose) after which you will breathe into the machine at regular intervals for up to 4 hours (you may want to bring some reading material along with you).  Free Wi-Fi is available in the department’s waiting room.

Depending on the results obtained from the initial test, you may be required to attend the department on one or two subsequent occasions during which you will be given a test solution of glucose and/or lactose.  After the test has finished you may go home or to work and resume your normal diet. 

What will happen afterwards?

The consultant in charge of your care will be informed of your results and will decide on your treatment plan.

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 624036

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 you, 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 you. 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 condition, the alternatives available to you, 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 you

We collect and use your information to provide you with care and treatment. As part of your care, information about you will be shared between members of a healthcare team, some of whom you may not meet. Your 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 you 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 doctor, or the person caring for you.

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 you. For further information visit the following page: Confidential Information about You.

If you or your carer needs information about your health and wellbeing and about your 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.

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