Measuring the levels of oxygen and carbon dioxide in the blood helps in the diagnosis and monitoring of many lung disorders. To measure these gases, a blood sample is taken from an artery, usually in the wrist. This test also measures blood acidity (pH), which may be abnormal in conditions such as diabetes mellitus and in some forms of poisoning. Oxygen levels in the blood can also be measured continuously using a pulse oximeter, which detects changes in the amount of light that blood absorbs.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.