Effect of predominant methanogenic flora on the outcome of lactose breath test in irritable bowel syndrome patients.

BACKGROUND: The relationship between hydrogen and methane production is a possible confounding factor in the interpretation of H(2) breath tests (HBT), but is usually disregarded for the interpretation of HBT and, in most instances, only H(2) excretion is measured. The present study was designed to evaluate the effect of predominant fasting methane CH(4) or H(2) production on the outcome of lactose HBT, in a large, homogeneous series of adult patients with irritable bowel syndrome (IBS). PATIENTS AND METHODS: A lactose HBT was performed in 237 IBS patients with predominant fasting methane production (CH(4)>H(2)), recording the outcome of the test, amount of gas excreted and occurrence of clinical symptoms. Data were compared to those of 237 age- and sex-matched IBS patients with low fasting CH(4) excretion. RESULTS: The test was positive in 124 predominant CH(4) producers (52.3%) (PMP), as compared to 201 (84.8%) low methane producers (LMP) (P<0.0001). Peak hydrogen concentration and area under the curve of H(2) were significantly (P<0.001) lower, and the occurrence of symptoms during the test less frequent, in PMP vs LMP patients. During the test, CH(4) excretion doubled in 57/113 (50.4%) patients with negative HBT, and in 49/124 (39.5%) with positive HBT. CONCLUSIONS: Patients with predominant fasting methane production excrete less H(2) than LMP, after an oral load of lactose. The lower prevalence of severe lactose intolerance in PMP, as well as lower incidence of symptoms during the test, is, indeed, related to lower and slower H(2) excretion. The assumption that H(2) excretion is an effective means of quantifying the amount of malabsorbed carbohydrates is questionable in PMP. Methane-producing patients likely have a higher 'false negative' rate as compared to LMP after an oral load of lactose. Nonetheless, as symptoms are related to the amount of gas produced in the colon, HBT identifies patients with 'lactose intolerance', irrespective of the presence of lactose malabsorption, and helps in predicting the effect of lactose-restricted diet.

Lactose malabsorption, irritable bowel syndrome and self-reported milk intolerance.

BACKGROUND: The relationship between lactose malabsorption, irritable bowel syndrome and development of intestinal symptoms is unclear, especially when the ingested dose of milk is small. Thus, the role of hydrogen breath testing in the diagnostic work-up of patients with nonspecific intestinal symptoms is still debated. AIMS: To establish the relationship between lactose malabsorption, severe self-reported milk intolerance, irritable bowel syndrome and related symptoms. METHODS: The prevalence of lactose malabsorption was prospectively assessed by means of a hydrogen breath test in 839 patients (503 with irritable bowel syndrome, based on the Rome criteria, regularly consuming milk, and 336 subjects who identified themself as milk intolerant, after an oral load of 25 g lactose). The test was considered "positive" when a hydrogen peak exceeding 20 ppm over baseline values was observed in two or more samples. Attempts were also made to establish whether the predominant presenting symptom (diarrhoea, constipation, alternating diarrhoea and constipation, pain and gaseousness) might be helpful in predicting the outcome of the breath test. RESULTS: The prevalence of a positive breath test was comparable in the two groups (337 patients with irritable bowel syndrome (66.9%) vs 240 patients with milk intolerance (71.4%)). The same holds true for the first peak of hydrogen excretion, total hydrogen output and prevalence of symptoms during, and in the four hours after, the test. The predominant presenting symptom was not useful for predicting outcome of the test either in regular milk users or in milk intolerant subjects. CONCLUSIONS: The almost identical results of the lactose breath test of patients with irritable bowel syndrome and subjects with self-reported milk intolerance suggests that the two conditions overlap to such an extent that the clinical approach should be the same. A lactose breath test should always be included in the diagnostic work-up for irritable bowel syndrome, as fermentation of malabsorbed lactose is likely responsible for triggering symptoms. Conversely, lactase deficiency is probably irrelevant in most subjects not affected by irritable bowel syndrome, within a moderate milk consumption.