Benefits of breath hydrogen testing after lactulose administration in analysing carbohydrate malabsorption.

BACKGROUND AND AIMS Breath hydrogen testing after lactulose administration may yield findings of clinical value, but whether it should be a routine part of breath testing has not been evaluated. We examined the contribution of breath testing after lactulose administration to the conduct and interpretation of breath hydrogen responses after fructose and lactose administration. METHODS Two hundred consecutive patients were given lactulose, fructose or lactose on separate days (at least 2 days apart); breath hydrogen was monitored every 15 min after the administration of each sugar. RESULTS Peak breath hydrogen levels after lactulose administration correlated with those after fructose (r = 0.26; P = 0.03) and lactose (r = 0.44; P = 0.004). Of the patients with a reduced response to lactulose, 51% had definite or borderline evidence of fructose malabsorption (FM); similarly, 23% of patients had definite or borderline lactose malabsorption. After lactulose administration, an increase in breath hydrogen levels occurred after the same amount of time or longer than after the administration of fructose or lactose (>120 min). The earlier the first rise in breath hydrogen levels after lactulose administration, the more frequently FM occurred, indicating an association between FM and rapid transit and/or small intestinal bacterial overgrowth. CONCLUSION Routine breath hydrogen testing with lactulose administration before other sugars cannot be used to define non-hydrogen producers, but might, by indicating the vigour of hydrogen production in the individual, allow more rational interpretation of results after testing with other sugars. It permits the duration of testing to be judged and provides information on possible mechanisms of FM.