Gregorio Peron, Stefano Dall’Acqua, Vincenzo Sorrenti, Maria Carrara, Stefano Fortinguerra, Giulia Zorzi, Alessandro Buriani

Lactose malabsorption is normally evaluated by measuring exhaled H2 produced by intestinal flora, from unabsorbed lactose. However, differing microbiome composition can lead to the production of CH4 instead of H2; hence, some authors challenge the H2 method sensitivity and favor the evaluation of both intestinal gases. To compare different approaches to usage of a lactose breath test for lactose malabsorption diagnosis, after medical evaluation of gastrointestinal symptoms. 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 H2 and CH4 analysis. Basal gas levels were subtracted from H2 and CH4 ppm and values at 4 hours and peaks were considered for analysis. Applying the standard methodology, which takes separately into consideration H2 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 H2 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. The threshold normally used for lactose breath test should be reconsidered and changed, merging H2 and CH4 stoichiometric values to increase sensitivity.