The Fructose-H2-Breath Test

The fructose-H2-breath test is used for the diagnosis of fructose-malabsorption. The test is absolutely contraindicated for patients with hereditary fructose intolerance. In this case the application of this diagnostic tool would be life-threatening. (The abundance of this metabolic
anomaly is of the order of 1:10 000 to 1:15 000. Symptoms are a hyperglycaemic shock after intake of food containing fructose (fruits, milk products containing saccharose, sweets etc.) in infancy, metabolic disorders accompanied by vomiting, fever and dystrophy, hepatomegalia and hepatic malfunctions. Diagnosis is possible on the basis of a deficiency of the subunit of the enzyme aldolase in the liver or the small intestinal mucosa.)

 Implementation of the fructose-H2-breath test:
After a nocturnal fasting period 25 g of fructose, dissolved in 250 ml of water, are orally administered. Breath samples are taken immediately before and 45, 90, 135 and 180 minutes after substrate intake. If H2-concentration ascends by more than D = 20 ppm, then fructose malabsorption must be assumed.

The Glucose-H2-Breath Test

Glucose is a monosaccharide rapidly and completely absorbed in the small intestine. In case of bacterial overgrowth in the small intestine absorption and bacterial fermentation compete with one another.

a) Normal.
Glucose is rapidly and completely absorbed in the small intestine and therefore does not arrive at the large intestine.

b) Pathologic.
Bacterial overgrowth of the small intestine. There and only there absorption and bacterial fermentation combined with hydrogen production compete with one another.
The glucose-H2-breath test is applied for diagnosing bacterial overgrowth of the small intestine, in combination with galactose-H2-breath test also for the diagnosis of glucose/galactose malabsorption. The test is also considered for the diagnosis of exocrine pancreas insufficiency.

Implementation of the glucose-H2-breath test:
After an overnight fast 75 g glucose, dissolved in 400 ml of water, is orally administered. Breath is sampled immediately before and 45, 90, 135 and 180 minutes after substrate intake.
If H2-concentration ascends by more than D = 20 ppm, then bacterial overgrowth of the small intestine must be assumed. Sensitivity and specificity of the glucose-H2-breath test, however, are only in the order of 60 to 90% or 75 to 100%, respectively. Nevertheless the test went its way for want of better alternatives.

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