Hydrogen breath test

Hydrogen breath testing (HBT) is used to detect lactose and/or fructose intolerance or small intestine bacterial overgrowth (SIBO). Traditionally HBT are performed in hospital due to the complexity and size of equipment but the development of the Gastro + Gastrolyzer allows for safe, accurate, portable near-patient HBT.

Indications for HBT

In patients with symptoms such as nausea, wind, bloating, abdominal discomfort and watery diarrhoea, which may be due to lactose and/or fructose intolerance or SIBO.

How it works

Hydrogen is produced when bacteria in the gut act on undigested carbohydrates such as lactose or fructose. The hydrogen gas passes across the gut wall into the blood stream and is carried to the lungs where it is expired.

In patients with lactose or fructose intolerance there is a rise in the amount of hydrogen detected over baseline which does not occur in normal subjects. When bacterial overgrowth of the small intestine is present, ingestion of lactulose results in two separate periods during the test in which hydrogen is produced, an earlier period caused by the bacteria in the small intestine and a later one caused by the bacteria in the colon.

The Gastrolyzer instantly and accurately measures the amount of hydrogen in a single expired breath sample. Disposable mouthpieces provide an anti-bacterial filter in addition to a one-way valve.

What are the limitations of HBT?

Some people do not have bacteria that produce hydrogen, and in these cases hydrogen breath testing is not possible. Most of these individuals have bacteria that produce a different gas, methane. Methane can be measured in the breath just like hydrogen but there is much less experience with methane, and the production of methane is more complex than the production of hydrogen. Therefore, it is not clear if the pattern of methane production after ingestion of sugars can be interpreted in the same way as hydrogen production.

Testing for bacterial overgrowth of the small intestine with lactulose cannot diagnose all cases probably due to the insensitivity of the test. In some people too rapid or too slow intestinal transit may decrease the effectiveness of the test and lead to a “false negative” result – i.e. where the person has SIBO but the HBT result is normal.

Any condition that results in the delivery of undigested dietary sugars to the colon may result in an abnormal HBT leading to a “false positive” result – i.e. where the HBT result is abnormal but is not due to lactose or fructose intolerance or SIBO. Pancreatic insufficiency and coeliac disease can cause abnormal breath tests, in the former instance because pancreatic enzymes that are necessary for the digestion of carbohydrates are missing, and in the latter instance because the lining of the small intestine is abnormal. It may be necessary to exclude these causes of abnormal breath tests by additional tests (pancreatic function tests and small intestinal biopsy).

How to do a HBT

Patients must not eat or drink (other than small amounts of water) anything on the morning of the test. There are dietary and drug restrictions before the test (see below). The test takes about 3 hours to perform. Before the test begins the patient blows into the Gastrolyzer to obtain baseline hydrogen level. The patient is then asked to drink a sugar solution (lactose, fructose or lactulose). Breath samples are taken every 15 minutes for first 30 minutes and then every 30 minutes for next 2 hours.

At the end of the HBT a hydrogen profile will be obtained, which will be interpreted by Dr. Harris.

Side effects

HBT is harmless and completely safe. Some patients may experience diarrhoea or abdominal cramping during or shortly after the test. This is not harmful and settles within a day or so. Loperamide (Imodium) may be used if needed.

Preparation for HBT

Avoid beans, peas, pulses, pasta and root vegetables for 48 hours before HBT (all increase amount of hydrogen produced in gut).

Teeth should be cleaned thoroughly before test. You will be asked to rinse your mouth with an antibacterial mouthwash before starting the HBT (bacterial in the mouth may produce hydrogen). This may be done at home after brushing your teeth: please let us know if you have done this already.

Do not chew gum before the HBT.

Cigarette smoking may lead to a false positive result due to carbon monoxide and must be avoided for 6 hours before HBT.

Broad spectrum antibiotics or bowel preparation (for colonoscopy, CT scanning, barium enema) may alter the bacterial content of the small and large intestine and must not be taken within 4 weeks of the HBT or a false negative result may be obtained.

Probiotics (e.g. lactobacillus, bifidus, acidophilus) in capsule, liquid or powder form are not allowed in the 4 weeks leading up to the HBT.

Avoid laxatives or stool softeners for 3 days before HBT.

At West Kent Gastroenterology, we work hard to provide our patients with top-class care. You will enjoy friendly, fast and modern treatment by a highly experienced gastroenterologist. We carefully review patient satisfaction and feedback, and at West Kent Gastroenterology we are continuously making improvements to our services, ensuring the highest level of care possible.

Clinic Locations

Spire Hospital
Fordcombe Road, Tunbridge Wells, Kent, TN3 0RD

Sevenoaks Medical Centre
London Road, Sevenoaks, Kent, TN13 2JD


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