The diagnostic potential of human breath has been appreciated for many years, yet the application of infrared spectroscopy for the detection of breath trace compounds is still in its infancy. Few diagnostic or investigative tests involving breath are based upon infrared spectroscopic techniques, its most prominent use to date being the detection of breath ethanol concentration for law enforcement. However, this is destined to change with the emergence of numerous infrared spectroscopic systems designed to measure stable isotope ratios in breath and the substantial market associated with such tests, e.g. the urea breath test for helicobacter pylori. This review article discusses the diagnostic potential and infrared spectroscopy of breath, several of its common features being illustrated with high-resolution spectra. An emphasis is placed on the recent development of instruments to perform isotope ratio breath tests with various approaches described and critiqued. Also the feasibility of using infrared spectroscopy to perform isotopic breath tests other than those based on is explored
