Frequently Asked Questions

Q. Why do people perform hydrogen breath tests?

Hydrogen breath testing is a relatively simple and non-invasive test to assist in the diagnosis of gastroenterological problems. Hydrogen breath testing can assist in confirming carbohydrate malabsorption or intolerance or ruling out these conditions. Carbohydrates which cannot be digested can cause stomach cramps, and diarrhoea as well as other symptoms such as bloating.

Q. What does a Hydrogen breath test show?

It shows the amount of hydrogen (H2 ppm) in the breath, which is an indirect non-invasive measurement of the amount possible carbohydrate malabsorption lactose, fructose sucrose and glucose) or intolerance, small intestinal bacterial overgrowth (SIBO) or estimation of oro-cecal transit time.

Q. How hygienic is the test?

MD Diagnostics recommend the use of SafeBreath filtered cardboard mouthpieces. SafeBreath have an in-built bacterial and viral filter ensuring >99% efficacy for a complete hygienic solution, protecting both patients and equipment.

Q. How is the test performed?

The patient should fast overnight for a minimum of 12 hours. The patient should be relaxed, and the test protocol and procedure explained clearly before the start of the test. The patient’s medication and health should be noted. Antibiotics can continue to distort test results for up to 4 weeks after they have been discontinued and laxatives should be discontinued at least 3 days prior to the test being performed. Prior to the breath test being performed the patient should ingest the specific test substrate – fructose, glucose, lactose, lactulose. The amount of substrate administered is dependent on the patient’s body weight, the substrate is dissolved in water for ingestion by the patient.

(Reference: Uday Ghoshal, How to interpret hydrogen breath tests. J.J. Neurogastoenterol Motil July 2011)

Q. How is the test performed?

After measuring the basal fasting value (0 minutes), the amount of hydrogen in the exhaled breath is measured at 30 minute intervals over the course of at least 2 hours,(or 3 hours dependent on the diagnostic reasoning for the test) plus an additional measurement at 15 minutes after the administration of the substrate.

Q. What is classed as a positive result?

A positive result is often considered to be an increase in hydrogen concentration of more than 20ppm above the basal value. A significant increase in exhaled hydrogen levels ad the appearance of symptoms both occurring at approximately 60 minutes after the start of the test are considered as a diagnosis of intestinal intolerance of the test substrate.

Q. What is classed as a negative result?

A negative result can be – no significant increase in hydrogen levels ie readings vary by less than 5ppm above or below the basal value, AND there are no symptoms.

If clinical symptoms occur but there is no increase in hydrogen it should be considered that the patient may be a non hydrogen producer, in order to make a safe diagnosis a lactulose test should be carried out. If a lactulose load still does not produce an increase in hydrogen levels, the subject is likely to a non-hydrogen producer.

Q. False positive results

False negative results may occur due to a longer oro-cecal transit time ie. It was possible that the test was terminated before a measurable increase in H2 levels could be established. If a slow transit time is suspected it is not unreasonable to continue to perform breath testing for a further 1 hour with 2 additional readings being performed.

Q. What may cause an elevated baseline reading?

An elevated baseline reading of approximately 15ppm, is usually because of incomplete fasting or a shorter fasting time than the requested fasting period.


  1. Implementation and interpretation of hydrogen breath tests. A. Eisenmann et al. J. Breath Res 2008
  2. How to interpret hydrogen breath tests. Uday Ghoshal J Neurogastroenterol Motil. Vol 17, No3 July 2011
  3. Use and abuse of hydrogen breath tests M Simre’n, P.O Stotzer. Gut 2006, 55:297-303


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