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Hydrogen Breath Test

Hydrogen Breath Test

General information

A hydrogen breath test provides information about the digestion of certain sugars or carbohydrates, such as milk sugar (lactose) or fruit sugar (fructose). This will help us to determine if you are intolerant to certain sugars. One example is the use of this test to detect lactose intolerance. The test is also used for detecting abnormal growth of bacteria within the small bowel by having the patient ingest lactulose.

Principles of Hydrogen Breath Testing: Hydrogen gas in the body is produced from intestinal bacteria. Bacteria, normally in the large intestine, produce hydrogen through fermentation of carbohydrates – such as lactose, lactulose, and fructose which are substrates given for the hydrogen breath test. Some of the hydrogen produced by bacteria is absorbed by the intestine whereby it enters the blood and is transported to the lungs. Hydrogen is then exhaled from the lungs by normal breathing. This is collected in the bag for subsequent analysis. In small intestinal bacterial overgrowth, the small intestinal bacteria ferment the sugars and produce an early rise in the breath hydrogen.

In lactose intolerance, the individual has a deficiency in lactase, the enzyme that breaks down lactose. Normally, lactose is broken down in the small intestine by lactase and very little lactose reaches the large intestine where the bacteria break it down to produce hydrogen. In lactose intolerance (lactase deficiency), the ingested lactose is not absorbed in the small intestine and reaches the colon where it is fermented by colonic bacteria producing a large amount of hydrogen, which is measured in the breath sample.

Preparation for the test

 • For four (4) weeks before your test: You should not take any antibiotics.

• For one (1) week before your test: Do not take any laxatives or stool softeners (for example Colace, Milk of Magnesia, Ex-Lax) or stool bulking agents (for example Metamucil or Citrucel). You should also not undergo any test that requires cleansing of the bowel, such as colonoscopy or barium enema.

• The day before your test: You may consume only the following foods and drinks: plain white bread, plain white rice, plain white potatoes, baked or broiled chicken or fish, a small amount of eggs, water, non-flavoured black coffee or tea. Only salt may be used to flavour your food. A little butter or margarine is permitted. Fizzy drinks such as lemonade or cola are not permitted. 

Do not eat or drink anything else: Eating prohibited foods could give false results for the test. Specifically, avoid beans, pasta, fibre cereals, fruit (including dried fruit) and high fibre foods. The night before the test, have an early dinner of rice and meat.

• For 12 hours before your test: Apart from water, you must stop eating and drinking 12 hours before the test. For example, if your test is at 9:00 a.m., you would stop eating and drinking at 9:00 pm the night before (see your appointment letter for precise timings). You may continue to take your usual prescription medicines with water until 12 hours before the test. Please bring all prescription medications to your appointment (or a list of them).

• The day of your test: Apart from up to 500ml (1 pint) of water, you should not eat or drink anything in the morning. You may take your essential medications with a small amount of water but do not take anything that may affect your bowel (if in doubt please ask). If you are diabetic requiring insulin or diabetic pills, ask your physician if you should change your morning dose. Generally, half of your normal long acting insulin is given. Oral hypoglycaemic medications are usually not taken that morning until completion of the test and resumption of eating meals. If in doubt please check with your referring Consultant. The morning of your test please brush your teeth but be careful not to swallow the toothpaste.

  • Do not eat, drink, chew gum, smoke cigarettes, eat breath mints or other sweets before or during the test.
  • Do not sleep or exercise while the test is being done. Your test may last for two to four hours. Please allow yourself sufficient time to complete your test. 

The Test Procedure: The Nurse or Clinical Scientist will verify that you have not had anything to eat or drink apart from water after midnight. A breath sample will be collected by having you exhale into the test machine. A glass of water mixed with either lactose, lactulose, or fructose will be given to drink. You should drink the whole amount.  Breath samples will be collected approximately every 15 minutes.  During the test, you should take notice of your symptoms and inform the technician if you have your typical symptoms for which the test is being performed.

During the test: You should not eat, chew gum, smoke, sleep, or exercise. When the test is over, generally after two or four hours, you may leave. You may return to your usual diet and activity after the test.

Are there any risks?

There are no serious risks from the tests; however, you may experience some symptoms during or after the tests. Some patients are quite sensitive to fermentation of sugars that are administered during tests or may have lactose intolerance and this can cause nausea, bloating and sometimes mild to moderate pain during or soon after the study. However, these symptoms are self-limiting and in the majority of patients settle within a few hours. If you have any concerns regarding symptoms you are experiencing then please contact us using the contact details given on this website. 

Going home

You will be allowed to go home after the test has finished. You do not need to take any special precautions after the test and you can eat and drink normally.