Reproducible lactulose hydrogen breath test as a measure of mouth-to-cecum transit time

Breath hydrogen monitoring after oral lactulose syrup is a conventional measure of mouth-to-cecum transit time (MCTT), but its reproducibility has been questioned. We compared the reproducibility of five measurements of MCTT after a conventional breakfast (380 kcal) taken with tea containing 20 g lactulose to five measurements of MCTT after 20 g lactulose in water in eight normal volunteers. Individual mean breakfast transit time was not significantly different from lactulose transit time in each of the seven subjects, but one had a breakfast transit time of 151±15 min and a lactulose transit time of 86±22 minutes (¯X ±sd, P<0.001). The coefficient of variation of breakfast transit time (11.6±5.3%, range: 6.9–24.2%) was less than that of lactulose transit time (30.7±7.8%, range: 22.1–50.0%, P<0.001). In a second set of experiments, the liquid phase marker (^99mTechnetiumdiethylene triamine pentaacetic acid) emptied from the stomach more rapidly after the lactulose solution (T1/2 16.3±5.4) than after the breakfast (33.9±10.9 min, P<0.01) and MCTT was shorter after lactulose (77±32 vs 104±40 min, trespectively, P<0.05). There was no correlation between MCTT of lactulose and breakfast and between half-time gastric emptying and MCTT of either lactulose or breakfast. We conclude that the ingestion of inert lactulose induces an abnormally rapid MCTT and that breakfast MCTT is a much more reproducible investigation and should be employed in studies requiring serial measurements.