Hydrogen Production Dynamics During Lactulose Breath Testing in Patients with Suspected SIBO

Background: Small intestinal bacterial overgrowth (SIBO) is characterized by excessive microbial colonization of the small intestine and is commonly diagnosed using hydrogen breath tests. However, most studies focus primarily on diagnostic thresholds rather than the overall dynamics of hydrogen production during the test. Methods: This cross-sectional study included 162 adults with chronic gastrointestinal symptoms who underwent a lactulose hydrogen breath test. Hydrogen concentrations were measured every 20 min over a 180 min period. Total hydrogen production was quantified using the area under the concentration–time curve (AUC), and hydrogen levels during the early (0–60 min) and late (>60 min) phases of the test were analyzed. Results: Among the participants, 100 (61.7%) were classified as SIBO-positive and 62 (38.3%) as SIBO-negative. Individuals with SIBO exhibited significantly higher total hydrogen production compared with those with a negative breath test result (mean AUC: 6938 vs. 2292 ppm × min, p < 0.001). Early hydrogen levels were also higher in the SIBO-positive group (8.7 vs. 4.5 ppm, p < 0.001). The most pronounced difference was observed during the late phase of the test, where hydrogen concentrations were markedly elevated in SIBO-positive individuals (52.7 vs. 12.0 ppm, p < 0.001). Conclusions: SIBO is associated with markedly increased hydrogen production during lactulose breath testing, particularly during the later stages of the test. These findings improve understanding of hydrogen production dynamics during lactulose breath testing and provide additional descriptive information regarding hydrogen response patterns; however, further studies are needed before clinical application. The observed differences should also be interpreted within the applied breath test classification framework.