Introduction Small bowel bacterial overgrowth (SIBO) is a condition defined as excessive bacterial load in the upper gut. SIBO can contribute to dyspeptic symptoms and altered bowel habit. The inappropriate fermentation of ingested nutrients in the upper gut produces gas (hydrogen and methane) and short chain fatty acids (SCFA’s), which can affect motility and sensation. Additionally colonic mal-fermentation is also thought to play a role in lower abdominal symptoms. This study attempted to assess symptom correlation to these disorders.

Method Lactulose hydrogen-methane breath testing was used to detect SIBO. Peak hydrogen and methane production was retrospectively evaluated in 463 patients following ingestion of 25 ml (16.5 g) lactulose with water. Breath samples were taken every 15 min for up to two hours and symptoms of bloating (BL), abdominal pain (AP) and nausea (NA) were tracked throughout. Assuming normal oro-caecal time, a rise in breath hydrogen/methane >10 ppm from baseline in the first 60 min of testing was defined positive for SIBO. A peak >60ppm from baseline between 60–120 min was defined as excessive caecal fermentation. Patients with a history of bowel surgery or previous treatment for SIBO were excluded from the analysis.

Results Data was available for 409/463 patients (162 Male, mean age 41, range 16–84). 288 (70.4%) had SIBO. At baseline, patients described symptoms of BL (323/409; 79.0%), AP (190/409; 46.5%), and NA (81/409; 19.8%). 228/323 (70.6%) with BL, 145/190 (76.3%) with AP and 66/81 (81.5%) with NA subsequently tested for SIBO. The prevalence of SIBO was similar in patients with diarrhoea (79/106; 74%) versus those with constipation (56/81; 69.1%; p > 0.05).

66/409 individuals (16.1%) had baseline methane levels >10 ppm. The likelihood of those with diarrhoea or constipation being methane producers was 8/106 (7.5%) and 25/81 (30.9%). 45/288 (15.6%) of individuals with SIBO were methane producers.

Caecal mal-fermentation, in the presence of reproduced symptoms, was observed in 48.4% of individuals with a diagnosis of SIBO and 9% of individuals without a diagnosis of SIBO.

Conclusion Although bloating was the most common symptom and nausea the least, nausea was more sensitive at indicating the presence of SIBO. Bowel habit did not appear to be useful at predicting SIBO. As expected, methane producers were more likely to have constipation with a significant percentage having concomitant SIBO. HMBT should be seen as a provocation test for patients with upper and lower bowel symptoms.

Disclosure of interest None Declared.