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This patient information leaflet is for patients who are doing a breath test at home. Please read it carefully before you start your test. Please complete your test within the next two weeks.

Breath tests are used to investigate bowel symptoms such as diarrhoea, bloating or abdominal discomfort. When we digest food gases such as hydrogen and methane are produced by the bacteria which live in the large bowel (colon).

Some of these gases pass out of your gut into the bloodstream and move to the lungs where they are exhaled in your breath. The amount of hydrogen and methane in a sample of your breath can be measured using a special monitor. We can use the change in the amount of these gases in your breath to test for bacterial overgrowth.

Small intestinal bacterial overgrowth (SIBO) occurs when bacteria which are normally present in the colon have moved into the small bowel. This is where glucose is usually absorbed.

Under normal circumstances the amount of hydrogen and methane in your breath will remain unaltered as the glucose drink, we give you is absorbed in the small bowel. If you have bacterial overgrowth, however, the glucose will be digested by the bacteria and produce gases which are released in your breath. By analysing your breath samples, we will be able to measure any increase in the hydrogen and methane in your breath.

Bacterial overgrowth usually occurs because of abnormal movement of the gut. It is most common in patients with illnesses which directly or indirectly affect the gut. It is less common in patients with no underlying illness.
The initial treatment for SIBO is a course of antibiotics. Most patients remain symptom-free. However, some people require a repeat dose of antibiotics. As a hydrogen/methane breath test is simple and non-invasive, we may repeat it to find out if the bacteria have been eliminated.

There are no risks involved with having a breath test. You may feel a little sick after you consume the drink needed for the test because we will ask you to fast before the test.

As with most tests, this test forms one part of the jigsaw of information which the doctor will collect to try to treat you as well as possible. If you do not wish to have this test for any reason, we will let your doctor know. Although it would be useful to have this information, they will continue to treat you as well as possible without it.

We will contact you by telephone to discuss the test. However, please contact us if you have any questions about how to prepare or how to do the test.

Four weeks before your test

Please do not take antibiotics for four weeks before your test. If you need to take antibiotics, please let us know and we will postpone your test. If you take antibiotics on an ongoing basis, please continue to take them but let us know on the day of your test.

Please do not take probiotics for four weeks before your test. This includes probiotic capsules, tablets, powders and liquids which you buy or which are prescribed for you. It does not include foods such as probiotic yoghurts and drinks, which you can continue.

One week before your test

Please stop medications which can affect gut movement, such as metoclopramide, prucaolpride, linaclotide and laxatives, for one week before the test. Please take all your other medications as normal.

Please leave at least three days following a colonoscopy before having your breath test.

The day before your test

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 avoid high fibre foods, for example, beans, pulses, lentils, vegetables such as broccoli and cauliflower and wholemeal products on the day before your test.

Please do not smoke for two hours before your test.

Brush your teeth as normal but do not use mouthwashes which contain alcohol.

If you are diabetic, please take into account 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.

During the test

Please do not eat or drink anything, except for small amounts of water, until the test has ended.

Do not smoke.

Do not exercise or increase your activity.

Do not use alcohol hand gel as this affects the breath monitor.

Make sure that you have your results sheet ready and that you have completed the pre-test checklist. Empty the bag of sugar (glucose) into a cup, add around 200ml of water and stir until the sugar has dissolved. Leave it to one side.

Record the date on the results sheet.

Pick up sample bag 1 and collect your first breath sample (see section 7). Record the time you took the sample on the results sheet.

Drink all the sugar and water mixture. You do not have to drink all of it in one go but try to finish it within three minutes. You can add more water if you find it difficult to drink or if there is sugar left at the bottom. Record the time you finish the drink on the results sheet.

Calculate the sample times for all the remaining samples and record them on the results sheet. You will need to take six samples – one sample before the drink, four after the drink at 20-minute intervals, and one final sample 10 minutes after the fifth sample. Therefore, if you finish the drink at 09:00, you need to take the next sample at 09:20 and so on. It may be helpful to set an alarm for taking the samples.

Take the samples at the calculated times. Do not worry if you are a little late taking your sample. If this happens cross out the planned sample time and record the actual sample time. Do not adjust the time for taking the next sample(s).

All samples should be taken in a resting, seated position.

Have one practice breath so that you have an idea of how long your breath out will be. Take a deep breath in, hold your breath for 15 seconds and then slowly and gently blow out.

The gas that we need for analysis is the very last part of your breath as you breathe out.

The sample bags we have sent you are numbered. Please use them in order i.e., 1, 2, 3…. There is also a spare bag in case one is damaged.

Each bag has a white plastic clip which is closed at one end and a clip which is left open at the other end. Always place your mouth onto the open end of the tube to breathe out into the sample bag. A clip may become undone so please make sure that each bag you use is closed at one end and open at one end.

Take a deep breath in and hold your breath for 15 seconds. Gently breathe out into the open air until you are at least halfway through your breath out, so that you have finished about half of the breath.

Then put the tube at the open end of the bag to your lips and breathe out so that the rest of your breath goes into the bag and the bag inflates.

The bag should be at least three quarters full, and you will have completely emptied your lungs.

If this is not the case, or you are not happy with the sample, please empty the bag and start again. You can practise as many times as you wish.

At the end of your breath out, snap the white clip near to your mouth shut so as to close the bag and prevent the breath escaping. Do this before you remove the tube from your mouth.

Please check that you fully close the white clip. This may be difficult whilst holding the bag and so once closed, it may help to put the clip onto a flat surface like a table and push down to ensure it is fully closed.

Squeeze the bag gently for several seconds to check that there is no leak. If there is a leak, use the spare bag

Put all the sample bags (used and unused) 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 information leaflet tells you about hydrogen/methane breath tests but if you have read the leaflet and have any queries, please contact the GI Physiology Unit.



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