breath testing

Collecting a breath sample and analysing it. Breath testing is useful in medicine to diagnose certain conditions. It is also used by the police to measure alcohol consumption (see Breathalyzer).

Many breath tests require the patient to consume a substance before the test, so that the breakdown products of this substance can be checked for. Abnormal quantities of the breakdown product indicate disease. For example, before a breath test to diagnose malabsorption syndrome (a condition characterized by severe chronic diarrhoea caused by the small intestine failing to absorb food efficiently) the patient must eat a dose of xylose, a sugar normally completely absorbed in the intestine. Large amounts of hydrogen in the breath within the next few hours reveal the disease is present.

Specific breath tests have been developed for a variety of diseases, including, in 2007, for lung cancer.

History Since the time of Hippocrates doctors have been aware that the odour of a patient's breath can aid diagnosis; for example the breath of a person with kidney failure smells similar to urine, and an undiagnosed diabetic's breath has a fruity odour.

In 1784 Antoine Lavoisier and Pierre Simon Laplace analysed the breath of a guinea pig, to reveal that it consumed oxygen and expired carbon dioxide.