Use of respiratory hydrogen (H₂) excretion to detect carbohydrate malabsorption

A technique in which an increase in the rate of breath H₂ excretion is used to detect carbohydrate malabsorption was tested. Ingestion of glucose, a completely absorbed sugar, never resulted in an increase in breath H₂ in normal subjects. In contrast, ingestion of xylose, an incompletely absorbed sugar, always yielded an increase in breath H₂. Assessment of lactose absorption with the use of breath H₂ measurements agreed closely with the results of standard lactose tolerance tests. This technique has advantages over the tolerance test in that: (1) it reflects the quantity of sugar that is not absorbed and, thus, is not influenced by gastric emptying rate or intermediary glucose metabolism, and (2) it is sufficiently sensitive to detect malabsorption of as little as 5 to 10 Gm. of carbohydrate.