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

ABSTRACT

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.