Table 2.

Biomarkers, sources and diseases.

Biomarkers	Sources	Diseases
Ammonia	Protein Metabolism	kidney failure, cirrhosis or hepatitis, hepatic encephalopathy, peptic ulcers, halitosis and asthma
Acetone	Acetoacetate Decarboxylation	Diabetes, lung cancer, dietary fat losses, congestive heart failure, brain seizure
Isoprene	Mevalonate Metabolism	disorders in cholesterol metabolism such as hypercholesterolemia
Methane	Intestinal bacteria metabolism of carbohydrates	Intestinal problems, colonic fermentation
Hydrogen Sulphide	metabolism of l-cysteine, cystathionine beta-synthase (CBS)	airway inflammation
Nitric Oxide	Nitric oxide Synthase	Asthma, acute lung injury, ARDS, inflammatory lung diseases, lung infection, lung cancer, rhinitis
Ethane	Peroxidation of polyunsaturated fatty acids	Oxidative stress, vitamin E deficiency, breast cancer, active ulcerative colitis
Pentane	Peroxidation of polyunsaturated fatty acids	Liver diseases, schizophrenia, breast cancer, rheumatoid arthritis, oxidative stress, acute myocardial infarction, asthma