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

Objective: To investigate the diagnostic value of a single hydrogen-methane breath test (SHMBT) for small intestinal bacterial overgrowth (SIBO). Method: 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 CH₄ (methane) and H₂ (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 U test,Spearman's Rank correlation analysis,and the Z test were used for statistical analysis. Results: Based on the international recommended diagnostic criteria for SIBO,which are fasting CH₄ ≥10 ppm (parts per million) or H₂ ≥20 ppm,the SHMBT-positive rate in the case group was significantly higher than that of control group (35.2% vs. 21.7%, χ²=4.08, P=0.043). Levels of CH₄ and H₂ were higher in the case group than in the control group [CH₄: 3(2,7) vs. 3(1,3) ppm, H₂: 11(4,22) vs. 10(5,15) ppm],and the difference in CH₄ levels was statistically significant (Z=6.22,P=0.001). ROC curves were generated based on whether the subjects had gastrointestinal symptoms. The areas under the ROC curves were 0.633 for CH₄ alone,0.531 for H₂ alone, and 0.620 for CH₄ combined with H₂. The cut-off values were fasting CH₄≥4 ppm,fasting H₂≥13 ppm,and fasting CH₄ ≥5 ppm (or CH₄≥4 ppm and H₂≥24 ppm),respectively. Measuring CH₄ alone and CH₄ combined with H₂ was effective for determining the presence of gastrointestinal symptoms (P<0.05). When CH₄ alone or CH₄ combined with H₂ 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 (P>0.05). The specificity of CH₄ alone was 79.9%,and the accuracy of CH₄ alone was 68.8%. The specificity of CH₄ combined with H₂ was 85.0%,and the accuracy of CH₄ combined with H₂ was 71.7%. Conclusion: Rapid one-time determination of CH₄ and H₂ in exhaled breath may a viable diagnostic method for SIBO, and using CH₄ combined with H₂ (i.e.,fasting CH₄≥5 ppm, or CH₄ ≥4 ppm and H₂ ≥24 ppm) as cutoff values may be feasible.