Unreliability of breath methane as a candidate indicator of functional bowel disorders.

Background/aims: The aim of this study was to examine the reproducibility of methane and hydrogen in exhaled air breath after a per-oral load of lactulose.

Methods: Methane was present in the exhaled breath of 21 of 50 healthy subjects recruited by advertisement. Three methane breath tests were performed in 12 women (aged 23.6+/-0.5 years, mean+/-SEM) after they consumed 10 g of lactulose dissolved in 300 ml of water. Short- and medium-term reproducibilities were assessed by paired examinations taken 3 and 17 days (median) apart, respectively.

Results: High values of coefficients of variation for paired examinations (CV(p)) indicated a poor short-term reproducibility of parameters characterizing either the methane or hydrogen excretion in breath air: CV(p) values of the maximum net increments over baseline in methane (max CH(4_net)), and in hydrogen (max H(2_net)), were 34% and 41%, respectively. Moreover, the reproducibility consistently deteriorated with increasing time gap between repeat measurements (CV(p): 60% for max CH(4_net) and 64% for max H(2_net)).

Conclusions: The low reproducibility of parameters characterizing quantitative methane breath excretion suggests that caution is necessary when judging the clinical usefulness of the methane breath test after a per-oral lactulose load for the purpose of diagnosing and classifying functional bowel disorders.