The  Lactose-H2-Breath Test

Lactose is a disaccharide. The enzyme lactase splits it to form galactose and glucose, which are absorbed in the small intestine.

a) Normal.
Lactose is split into galactose and glucose and then absorbed in the small intestine. In normal fermentation by anaerobic microorganisms therefore proceeds either not until the large intestine or not at all.

b) Pathologic
(lactose malabsorption, lactose intolerance). For want of lactase the test substance is neither split into the monosaccharides nor absorbed in the small intestine. Therefore the substrate is fermented to form hydrogen not until the large intestine. There this hydrogen is absorbed through the intestinal wall and then dissolved into the bloodstream, released into the lungs through the capillary blood vessels surrounding the alveoli and finally expired.
The lactose-H2-breath test is used for the diagnosis of lactose malabsorption, which is highly abundant all over the world. The test is also applied to control the therapy of lactose intolerance by loperamide.

Implementation of the lactose-H2-breath test:
For diagnosing lactase deficiency 2g/kg (maximum 20g) lactose, dissolved in 100 ml of water, are orally administered after an overnight fast. Breath samples are taken immediately before and 30, 60, 120 and 150 minutes after substrate ingestion. We recommend a cut-off value of ? = 30 ppm for distinguishing patients with lactase deficiency and normals.
Sensitivity and specificity are then in the range of 90 to 96%. If additional symptoms like abdominal pain are reported, lactose intolerance may be assumed. Starting 24 hours before substrate uptake and during the test beans, pies, larger amounts of apples, onions, cabbage, bread fresh from the oven and other heavy food must not be taken in.

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