Retrospective analysis of a lactose breath test in a gastrointestinal symptomatic population of Northeast Italy: Use of (H2+2CH4) versus H2threshold

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 CH4 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 CH4 analysis. Basal gas levels were subtracted from H-2 and CH4 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 CH4 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 CH4, 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 CH4 stoichiometric values to increase sensitivity.