Evaluating breath methane as a diagnostic test for constipation-predominant IBS.

Studies suggest that subjects with IBS have altered gut flora. Among these findings, methane production is more commonly associated with constipation-predominant symptoms. In this study, we prospectively evaluated the role of methane as a diagnostic test. Consecutive Rome I positive IBS patients referred for a lactulose breath test were eligible to participate. After exclusion criteria, subjects completed a symptom questionnaire grading bloating, diarrhea, and constipation on a VAS scale (0-100 mm). Once completed, a physician interviewed the subjects and rated the subject accordingly, and also determined whether the patient had C-IBS, D-IBS, or neither. Subjects and physicians were blinded to the results of the breath test. The presence of methane in the breath test was compared to the results of the scoring by subjects and physicians. A total of 56 Rome I positive IBS subjects were enrolled. During breath testing, 28 subjects produced methane. Good agreement between physician's evaluation and the patient's was seen (diarrhea = 0.69; constipation = 0.69; bloating = 0.62). The severity of constipation was noted to be greater in the methane group (49.3 +/- 28.7) than in the non-methane group (25.3 +/- 31.47) (P < 0.01). In contrast, diarrhea was less severe in the methane group (12.3 +/- 21.0) than the non-methane group (36.7 +/- 32.4) (P < 0.01). Out of the 56 patients, 23 C-IBS subjects were identified by the physician. When methane was used to predict the assignment of C-IBS compared to non-C-IBS, it had a sensitivity of 91.7% and a specificity of 81.3% (OR = 47.7, CI = 9.4-232, P < 0.00001). In conclusion, methane is a potential diagnostic test for the identification of C-IBS and may guide treatment.