Hydrogen / methane breath test for fructose / lactose malabsorption – Testing at home

Fructose is a sugar which is found naturally in fruits. It is normally absorbed in the small bowel but if not fully absorbed, it can lead to symptoms of cramping, bloating, and diarrhoea. Symptoms vary depending on the person and the amount of fructose they have eaten. Fructose malabsorption can occur in people with no other underlying illnesses.

Lactose is a sugar which is found in milk and dairy products. Some people are unable to digest lactose because they do not produce enough of an enzyme called lactase. Enzymes are substances which help to break down food. When the undigested lactose reaches the large bowel it can cause symptoms of cramping, bloating and diarrhoea. Lactase deficiency occurs in approximately 1 in 20 of the UK population, but rates differ in different ethnic groups. Symptoms may vary depending upon the amount of lactose you eat. Lactose intolerance may occur in people with no other underlying illnesses.

There are no risks involved with having a breath test. If you are diabetic, please see 'How do I prepare for my breath test?' below. 

There are no alternative tests to investigate these issues at UCLH. If you decide not to do this test, we will let your referrer know who will then discuss follow-up options with you.

Medications: 

• Do not take probiotics for 4 weeks before the test. Probiotic foods such as yogurt or fermented foods are not included and can be eaten. 
• Do not take antibiotics for 4 weeks before the test. If you are on a short course, then please continue the medication and complete the test 4 weeks after finishing. If you routinely take daily antibiotics, you do not need to stop them before doing the test. 
• Do not take laxatives for 1 week before the test (if you only take them occasionally). If you routinely take laxatives daily, continue to take these and stop 24 hours before the test. 
• Do not take medications that affect your gut motility for 24 hours before the test (e.g. metoclopramide, prucalopride, baclofen). 

The day before and day of your test: 

• Please avoid high fibre foods e.g. beans, pulses, lentils, vegetables such as broccoli and cauliflower, and wholemeal products. 
• Please do not have anything to eat or drink (except for water) for 13 hours before your test. Please do not chew gum. We suggest you complete your breath test in the morning, so this usually means fasting overnight and missing breakfast.  
• Please do not smoke for two hours before your test.  
• Brush your teeth as normal but do not use mouthwashes which contain alcohol. 

During the test: 

• Do not eat or drink anything. Do not smoke. Do not exercise or increase your activity. 

NB: If you are diabetic, please consider the fact that you will be drinking the equivalent of a medium or small sized carbohydrate meal (75g of glucose). If you are insulin dependent, you may need to alter your dose accordingly.

Please contact us if you have any problems or queries. 

Each sample bag should have a white clip on one end and a blue stopper on the other. If you have been given a bag of white clips and a bag of blue stoppers, please place a clip on one end and a blue stopper on the other, for each sample bag. Each bag should look like this: 

• All samples should be taken in a resting, seated position. Take a deep breath in and hold for as long as you can, up to 15 seconds.
• Gently breathe out into the open air until you have exhaled approximately 50-75% of your breath. This is because we only want the end part of your breath in the bag.
• Place your lips around the tube which has the white clip on and exhale the end of your breath into the bag.
• Once you have exhaled completely into the bag, clip the white clip closed immediately to seal the gas in the bag. Do this before you remove the tube from your mouth.
• You can practice this as many times as you wish before you begin the test. You can use any bag to practice, just ensure you empty it again afterwards.

1. Make sure that you have your results sheet ready and that you have completed the pre-test checklist and recorded the date.  
2. Pick up sample bag 1 and collect your first breath sample (see 'How do I take a breath sample?' above). Record the time you took the sample on the results sheet. This is your fasted or baseline breath. 
3. Mix the substrate (lactose or fructose) with around 200ml of water (this does not have to be exact). Drink all the sugar and water mixture. Please finish it within three minutes. Record the time you finish the drink on the results sheet. 
4. Perform the next sample (bag 2) 20 minutes after the drink is finished. Each sample (bags 3-10) is then taken at 20-minute intervals. It would be helpful to write down the timings for each sample and set an alarm. An example results sheet is given on the opposite side of your results sheet. Please ensure you complete the bags in order from 1 to 10.

Put all the sample bags and your results sheet back into the box which they came in and close the box. Please return your box within one week of completing your test. 

Please bring your box back to the GI Physiology Unit during our opening times and hand it in at reception. We are open 09:00-17:00, Monday to Friday. 

If you wish to post your samples back to us, you will need to take your box to the Post Office and pay for return postage. Please use the return address label in your box, not the address in this leaflet. Please send your box by normal post, not recorded delivery. 

Sometimes you may need to do another breath test after the first one has been analysed, but before your result is finalised. If this is needed, we will tell you this when we telephone you after we have analysed the first test.

We will analyse your samples and put the test results into a report which will be sent to your referring doctor. A copy will also be saved onto the hospital system and sent to you and to your GP. When you return to see your doctor (for example at the outpatient clinic at the Trust, at another hospital, or your GP surgery) the test results and any treatment will be discussed with you.

You will be able to continue with your normal activities after the test. Please contact us if you have any problems.

This page tells you about hydrogen / methane breath tests but if you have read the page and have any queries, please contact the GI Physiology Unit. 

Address: GI Physiology Unit, Lower Ground Floor, EGA Wing University College Hospital, 25 Grafton Way London, WC1E 6DB

GI Physiology Administrator: 020 3447 9130 (Monday to Friday 09:00 to 17:00)

Switchboard: 020 3456 7890 / 08451 555 000, ext. 79130

Email: UCLH.GIphysiology@nhs.net

The GI Physiology Unit is on the lower ground floor of the EGA wing. You do not need to come to the hospital for your test.