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

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.

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.

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)).

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.