393 Optimising Post-Surgical Assessment for SIBO

Abstract Introduction The postsurgical screening for small intestinal bacterial overgrowth (SIBO) based on hydrogen breath test (BT) can be equivocal which may require optimising. Method BTs were performed using 20g of lactulose and studies conducted between January and June of 2025 were reviewed. Breath samples were collected at fasting phase and postprandially (for 3-hours) which were analysed for hydrogen and methane compositions. Hypothesis testing was computed using fisher exact test. Results 41 patients (15.1%)(female:male=30:11, age 27-79 years) had general surgery of the foregut (n=33), midgut (n=9) and hindgut (n=10)(11 patients had multiple regional surgeries). Methanogenic Archaea (MA) and absent colonic fermentation (ACF) were more prevalent than SIBO, which may contribute to the false-negative screening of SIBO. MB oxidise the ambient hydrogen as fuel source for energy, thereby reducing hydrogen concentration in breath samples. Higher prevalence of SIBO was detected in the absence of MB (20.7% vs 8.33%, p-value 0.651). In addition, higher prevalence of SIBO is affiliated with colonic fermentation of the indigestible lactulose whilst ACF is affiliated to negative SIBO screening (38.9% vs 0.0%, p-value 0.001). Conclusions Nearly have of the SIBO screening in patient with general surgery are prone to false-negative outcomes and require optimised screening from the complex clinical nature.Negative SIBO in the presence of MA require repeat screening post treatment for MA.Negative SIBO in the ACF may require gut transit investigation and extending the screening for SIBO tailored to the oro-caecal transit time.