Retrospective analysis of a lactose breath test in a gastrointestinal symptomatic population of Northeast Italy: use of (H(2)+2CH(4)) versus H(2) threshold

BACKGROUND: Lactose malabsorption is normally evaluated by measuring exhaled H(2) produced by intestinal flora, from unabsorbed lactose. However, differing microbiome composition can lead to the production of CH(4) instead of H(2); hence, some authors challenge the H(2) method sensitivity and favor the evaluation of both intestinal gases. AIM: To compare different approaches to usage of a lactose breath test for lactose malabsorption diagnosis, after medical evaluation of gastrointestinal symptoms. METHODS: In a retrospective observational study, we compared the 2 approaches in a population of 282 subjects in Northern Italy. Following oral lactose administration, exhaled samples were harvested every 30 minutes for 4 hours and prepared for H(2) and CH(4) analysis. Basal gas levels were subtracted from H(2) and CH(4) ppm and values at 4 hours and peaks were considered for analysis. RESULTS: Applying the standard methodology, which takes separately into consideration H(2) and CH(4) produced in the intestinal lumen, the results indicated that 11.7% of the patients were diagnosed “positive” for hypolactasia, differently from what was expected. Conversely, taking into consideration the sum of H(2) and CH(4), the percentage increased to 62.8%, closer to the expected one. No significant differences were found when comparing the 2 groups for age, gender, or symptoms. The sizable difference between the 2 approaches is likely linked to gut microbiome variability, and consequently the different production of the 2 gases, in the population. CONCLUSION: The threshold normally used for lactose breath test should be reconsidered and changed, merging H(2) and CH(4) stoichiometric values to increase sensitivity.