Figure 3.

The lactulose hydrogen breath test (LHBT) predominantly measures small intestinal transit rather than small intestinal bacterial overgrowth (SIBO) in irritable bowel syndrome (IBS) patients. Upper schematic shows ingestion of test meal with subsequent serial measurement of both H₂ gas, resulting from fermentation of the lactulose by intestinal bacteria, and Tc⁹⁹ scanning in the caecum. This latter measurement detects when the test meal has reached the caecum. The stylised drawing below shows a representative result from an IBS patient with serial measurements over time. The Tc⁹⁹ had already reached the caecum in large quantities before the H₂ PPM level has reached the threshold for an abnormal test. This demonstrates that the increased H₂ production results from fermentation by colonic bacteria, not by abnormal bacteria small intestine (ie, SIBO).⁹⁴