143 Reviewing Small Intestinal Bacterial Overgrowth Testing in Patients with Abdominal Surgery

Abstract Introduction Symptomatic patients post abdominal surgery may be referred for hydrogen breath test (BT) to screen for small intestinal bacterial overgrowth (SIBO). This study reviews the complex nature of the outcomes. Method BTs were performed in accordance to Bedfont Scientific guidelines (20g Lactulose was used and Gastrolyzer analysed the breath samples). Patient undergoing BT post abdominal surgery between January to June 2025 were reviewed. Results 51 patients (18.8%)(female:male=37:14) had abdominal surgery (surgery of foregut 14, midgut 18, hindgut 11, gynaecological surgery 7, exploratory laparotomy 3 and nephrectomy 1. 15 patients had multiple surgeries form the list). 39 patients (76.5%) produced exceptional end-tidal breath samples from average oxygen concentration found <15%. SIBO was unequivocally positive in 11 patients (21.6%) with maximum hydrogen rise from baseline by 109PPM [95%CI: 38.5-80.7PPM], which was captured within 90-minutes. 2/11 patients (18.2%) had SIBO co-existing with gastrointestinal methanogenic archaea (MA). In total, 12 patients had MA (23.5%) which oxidise ambient hydrogen as fuel source for energy and produce methane. Thereby reducing the hydrogen production expelled in BT and producing false-negative detection for SIBO. Furthermore, 19 patients (37.3%) in the absence of MA demonstrated no evidence of colonic fermentation of the indigestible lactulose by 180-minutes (hydrogen rise <20PPM). This is suggestive of a slow gut transit which can also falsify negative for SIBO. Conclusions Half of the patients with past abdominal surgery may have false-negatives for SIBO and require repeat testing after treating other causes.