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Carbohydrate in the gut lumen can be fermented by bacteria in the small intestine forming hydrogen as one of the bye-products . Some of this hydrogen is absorbed into the blood stream and there is a direct relationship between the hydrogen concentration in expired breath and the amount of unabsorbed carbohydrate in the intestine.

In clinical situations in which there is poor digestion and or absorption of carbohydrates breath hydrogen concentrations increase 4-6 hours after eating. If a patient has bacterial overgrowth the increase in breath hydrogen is detected only 1-2 hours after eating.

Expired air is collected into a sealed plastic container by application of an anaesthetic mask to the face or, in the case of cats and smaller dogs, by confining the animal to a sealed Perspex box with an air supply and air outlet for collection. Serial collections of expired air are taken at regular intervals following a meal and air analysis is performed using standard techniques.

Typical results following direct collection through a face mask:

  • Healthy fasted dogs : breath hydrogen 0.9 +/- 0.1 ppm - peak at 1.4 +/- 0.2 ppm 8 hours after feeding.
  • Dogs with chronic small intestine disease : fasting hydrogen - 5.3 +/- 1.3 ppm - peaks at 72.2 +/- 18 ppm 7 hours after feeding.
  • Dogs with exocrine pancreatic insufficiency : fasting hydrogen - 3.3 +/- 0.9ppm - peaks at 28.8 +/- 2 ppm 6.5 hours after feeding.

(Results reproduced from "Small Animal Gastroenterology" by Strombeck & Guilford with permission from Harcourt Brace Publishers.)

Last updated : January 2016