Breath diagnostics involves the analysis of a sample of human breath to monitor, diagnose, and detect diseases and conditions. Besides its primary constituents – nitrogen, oxygen, carbon dioxide and water vapour – exhaled human breath contains over one thousand other compounds at trace levels. Many of these species are formed as the by-products of metabolic processes and can be indicative of a number of different diseases and conditions. Examples of such biomarkers are outlined below: Breath diagnostics involves the analysis of a sample of human breath to monitor, diagnose, and detect diseases and conditions. Besides its primary constituents – nitrogen, oxygen, carbon dioxide and water vapour – exhaled human breath contains over one thousand other compounds at trace levels. Many of these species are formed as the by-products of metabolic processes and can be indicative of a number of different diseases and conditions. Examples of such biomarkers are outlined below: Acetone - Diabetes mellitusAmmonia - Renal DiseaseHydrogen Sulfide - Liver CirrhosisMethane - Colonic Fermentation Diabetes mellitus is a serious chronic illness that affects how the body uses food, and is a life-threatening human disease if left untreated. It affects more than 171 million people worldwide. Diabetes mellitus can be subdivided into; type I diabetes, where the body does not produce insulin, the hormone which facilitates the uptake of glucose by cells; and type II diabetes, where the body becomes resistant to insulin, thus inhibiting the extent of glucose usage. In each case, the ineffective use of glucose as a source of energy leads to the subsequent breakdown of fatty acids to compensate. This consumption of fatty acids by ketosis, produces acetone which is excreted into the blood, before equilibrating with air in the lungs. Diabetes may therefore be characterised by elevated breath acetone levels.There are several new technologies being developed to diagnose and monitor diabetes by means of an acetone breath test. It is hoped that the breath test will one day supersede the use of finger-prick blood tests and provide non-invasive diabetes monitoring. These technologies include Cavity Enhanced Absorption Spectroscopy (CEAS) and Plasma Emission Spectroscopy (PES).