H₂/CH₄/H₂S

H₂ ：

Biomarker of microbial metabolism for the diagnosis of gastrointestinal diseases such as SIBO and carbohydrate maldigestion

Produced by H₂-producing bacteria via microbial fermentation.

CH₄ ：

Biomarker of microbial metabolism , especially for constipation and/or bloating

Produced by CH₄-producing archaea or bacteria for H₂ disposal.

H₂S*：

Biomarker of microbial metabolism for diagnosis of SIBO - Diarrhea

Produced by sulphate-reducing bacteria via H₂ consumption.

References:
[1]Methodology and indications of H₂-breath testing in gastrointestinal diseases: the Rome Consensus Conference.Aliment Pharmacol Ther. 2009. Aliment
Pharmacol Ther. 2009. 29 Suppl 1:1-49.
[2] Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus.Am J Gastroenterol. 2017 May;112(5):775-784.
[3] ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth.Am. J. Gastroenterol., 2020, 115: 165-178.