Reevaluating our understanding of lactulose breath tests by incorporating hydrogen sulfide measurements

Background and Aim: Breath testing has become a commonly used tool in gastroenterology to evaluate changes in the fermentation pattern of the gut microbiome. Currently, hydrogen and methane gas concentrations are measured in breath testing and evaluated against specific cut-off values for interpretation as normal or abnormal. However, microbial gas kinetics is a complex process that is not currently fully considered when interpreting breath gas results. Gas exchange between hydrogen producers and hydrogen consumers (methanogens and sulfate-reducing bacteria) is a process whereby hydrogen availability is determined by both its production and removal. Hydrogen sulfide is a crucial gas involved in this process as it is a major hydrogen-consumptive pathway involved in energy exchange. Methods: This is a cross-sectional study evaluating lactulose breath testing with the inclusion of hydrogen sulfide measurements in patients referred for breath testing for gastrointestinal symptoms of bloating, excessive gas, and/or abdominal pain. Results: A total of 159 patients were analyzed between October 2016 and June 2017. Mean hydrogen concentrations with a positive trend through a 3-h period (R-2 = 0.97), mean methane concentrations with a positive trend (R-2 = 0.69), and mean hydrogen sulfide concentrations with a negative trend (R-2 = -0.71) were observed. Conclusion: By incorporating energy exchange in the interpretation of the lactulose breath test, we reevaluated specific breath gas profiles, including those commonly described as "hydrogen nonproducers" and the "double-peak" phenomenon.