Evaluation of hydrogen excretion after lactulose administration as a screening test for causes of irritable bowel syndrome.

Objective: To determine whether it is possible to separate cases of irritable bowel syndrome associated with excess total hydrogen production (as a surrogate of colonic fermentation; these patients may be offered an exclusion diet as treatment) from other causes of irritable bowel syndrome by determining the amount of hydrogen excreted on patients' breath after oral administration of lactulose.

Design: Comparison of 24-hour hydrogen excretion and breath hydrogen following lactulose in untreated patients fulfilling the Rome criteria for irritable bowel syndrome, normal controls and irritable bowel syndrome patients who had previously failed to improve on an exclusion diet.

Methods: Colonic fermentation was measured by indirect calorimetry over 24 h. Immediately after calorimetry, the patients who were fasting received 20 g lactulose; end-expiratory breath samples were then collected every 30 min for 3 h. Hydrogen concentrations were determined by an electro-chemical cell.

Results: The total 24-hour excretion of hydrogen was significantly greater in the irritable bowel syndrome group (median 333.7 ml/24 h, interquartile range 234.7-445.67) compared to the normal volunteers (median 203.1 ml/24 h, interquartile range 131.4-256; P = 0.002) or the failed-diet group (median 204.5 ml/24 h, interquartile range 111.35-289.13; P = 0.015). No difference was detected in breath excretion of hydrogen following lactulose in any group.

Conclusion: Total hydrogen production over 24 h is increased in some patients with irritable bowel syndrome who may respond to exclusion diets. However, this sub-group of patients cannot be identified by measuring breath-hydrogen excretion after lactulose.