[The exhaled hydrogen test: its value in the quantitative diagnosis of carbohydrate malabsorption].

A study has been conducted to determine the accuracy of breath-H2 measurements for quantitating the malabsorption of small amounts of carbohydrate. H2 pulmonary excretion was measured after an overnight fast at 30-min intervals for 4 h in 7 healthy subjects after ingestion of 4 doses of lactulose (2.5,5,10 and 50 g). In 3 subjects the test was repeated without lactulose. The volume of H2 excreted was directly proportional to the amount of ingested lactulose: mean cumulative H2 excretion over a 2-h period after 5, 10 and 50 g was 2.9, 6.6 and 37.6 ml H2 respectively; H2 response after the 2.5-g dose was not perceptible. Individual H2 excretion before lactulose ingestion was highly variable: 0.096 +/- 0.075 mlH2 (mean +/- 1 SD); the individual base line rate over a fasting period showed marked fluctuations. It is concluded that the inter- and intraindividual variations of H2 excretion limit the accuracy of the H2 breath test for quantitating malabsorption of small amounts of carbohydrate.