The effect of dose and osmolality of lactulose on the oral-caecal transit time determined by the hydrogen breath test and the reproducibility of the test in normal subjects.

The lactulose hydrogen breath test was used to determine the oral-caecal transit time in healthy volunteers. An inverse relationship between the dose of lactulose ingested and the oral-caecal transit time was found. The osmolality of the lactulose solution did not effect the transit time. Results obtained from the test were found to be reproducible in normal subjects. Standardization of the meal and what constitutes a sustained rise in the breath hydrogen excretion following administration of lactulose are essential in the valid interpretation of this test as a measure of oral-caecal transit time.