Hydrogen Breath Test to Diagnose Lactose Malabsorption: Milk, Lactose and Osmotic Effect

Purpose: There is no gold standard to diagnose lactose malabsorption. The hydrogen breath test is the most widely used, but many methodological points need to be standardized. Our aims were to verify (a) whether the use of milk rather than lactose solution improves accuracy, and (b) whether different concentrations of the lactose solution modify the results. Materials and Methods: 33 healthy volunteers underwent the H2 breath test after 400 ml of semi-skimmed milk and after an oral solution containing 20 g of lactose in 400 ml of water; a second group of 38 healthy volunteers underwent the H2 breath test after 400 ml of semi-skimmed milk and after an oral solution containing 20 g of lactose in 200 ml of water. Basal gastrointestinal transit was evaluated with radio-opaque markers. Results: In 31 out of 33 subjects H2 breath test results were concordant after milk and 20g of lactose in 400 ml of water. Two subjects were positive after lactose, but negative after milk. The time at which the test became positive was earlier after lactose than after milk. The administration of a more concentrated lactose solution increased discrepant results, as in 5 subjects out of 38 the H2 breath test was negative after milk and positive after lactose solution. Basal gastrointestinal transit time did not show any significant difference between positive and negative subjects. Conclusions: To diagnose lactose malabsorption, milk is a more physiologic substrate for the H2 breath test. Lactose solutions induce an osmotic effect which can cause false positive results.