[Simultaneous Measurement of Hydrogen and Methane Improves Diagnostic Yield in the Diagnosis of Intestinal Microbial Overgrowth].

Introduction. Breath tests have been widely used for the diagnosis of small intestinal microbial overgrowth. Some of the equipment currently used for gas measurement tends to have limitations; the simplest portable equipment measures only hydrogen, while the most complete ones allow the simultaneous measurement of hydrogen, methane, CO2, and recently hydrogen sulfide. The presence of elevated methane values usually coincides with decreased hydrogen excretion and, therefore, by measuring only exhaled hydrogen levels, the study is reported erroneously as normal. Aim: . To analyze the comparative diagnostic yield between the isolated measurement of hydrogen and the simultaneous measurement of hydrogen and methane. Material and methods: . An observational study was carried out by analyzing hydrogen and methane concentrations in exhaled air, using lactulose as substrate. The study included 353 patients (78% women), with an age range of 18/75, who presented one or more of the following symptoms: abdominal pain, bloating, flatulence and chronic defecatory problems. Values ≥ 20 ppm for hydrogen within 90 minutes lactulose of ingestion were considered positive, and for methane, values ≥ 10 ppm at any time during the study. The diagnostic yield was calculated using the formula: number of positive studies divided by the total number of studies performed. Based on the normal reference values, the number and percentage of diagnoses of small intestinal bacterial overgrowth, intestinal methanogenic overgrowth and mixed microbial overgrowth were calculated. Results: . Out of a total of 353 patients, 111 (31.44%) were LBT positive; 78 (22.09%) had mixed flora (SIBO + IMO); 54 (15.29%) had methanogenic overgrowth; 55 (15.62%) had small intestine bacterial overgrowth, (accepted as a positive hydrogenic response exclusively) and 55 (15.62%) were negative. Fifty-four (15.29%) had a flat curve. The diagnostic yield varies if we consider only positive SIBO by exclusive hydrogen measurement, in such cases it was 0.16 (95% CI 0.12-0.19). However, when considering mixed cases (partial diagnosis) the diagnostic yield was 0.47 (95% CI 0.41-0.52). On the other hand, the simultaneous measurement of hydrogen and methane added was positive for those with methanogenic overgrowth (111+55+78/353) and the diagnostic yield is 0.69 (CI 0.64-0.73). Conclusion. The simultaneous measurement of H2 and CH4 would improve the diagnostic yield compared to the isolated measurement of hydrogen.