[Single hydrogen-methane breath test for the diagnosis of small intestinal bacterial growth].

To investigate the diagnostic value of a single hydrogen-methane breath test (SHMBT) for small intestinal bacterial overgrowth (SIBO). The current investigation was a cross-sectional study. Questionnaires and SHMBTs were administered to 162 patients with gastrointestinal symptoms (case group) and 69 healthy volunteers (control group). Differences in SHMBT results between the two groups were assessed,and cut-off values of CH (methane) and H (hydrogen) were analyzed via receiver operating characteristic (ROC) curves. Lastly,archived SHMBT data from 2 655 patients with gastrointestinal symptoms (validation set) were used to evaluate the diagnostic value of the SHMBT with respect to SIBO. The Chi-square test,the Mann-Whitney test,Spearman's Rank correlation analysis,and the test were used for statistical analysis. Based on the international recommended diagnostic criteria for SIBO,which are fasting CH ≥10 ppm (parts per million) or H ≥20 ppm,the SHMBT-positive rate in the case group was significantly higher than that of control group (35.2% vs. 21.7%, =4.08, =0.043). Levels of CH and H were higher in the case group than in the control group [CH: 3(2,7) vs. 3(1,3) ppm, H: 11(4,22) vs. 10(5,15) ppm],and the difference in CH levels was statistically significant (=6.22,=0.001). ROC curves were generated based on whether the subjects had gastrointestinal symptoms. The areas under the ROC curves were 0.633 for CH alone,0.531 for H alone, and 0.620 for CH combined with H. The cut-off values were fasting CH≥4 ppm,fasting H≥13 ppm,and fasting CH ≥5 ppm (or CH≥4 ppm and H≥24 ppm),respectively. Measuring CH alone and CH combined with H was effective for determining the presence of gastrointestinal symptoms (<0.05). When CH alone or CH combined with H were used as diagnostic indicators of SIBO, the respective SHMBT-positive rates in the validation set were 34.2% and 30.4%. These rates did not significantly differ from the SIBO-positive rate of 32.0% obtained via the international recommended diagnostic criteria (>0.05). The specificity of CH alone was 79.9%,and the accuracy of CH alone was 68.8%. The specificity of CH combined with H was 85.0%,and the accuracy of CH combined with H was 71.7%. Rapid one-time determination of CH and H in exhaled breath may a viable diagnostic method for SIBO, and using CH combined with H (,fasting CH≥5 ppm, or CH ≥4 ppm and H ≥24 ppm) as cutoff values may be feasible.