Test: Measuring Blood Gases

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.

Taking blood

To obtain a blood sample, the skin is cleaned and a local anaesthetic may be given before the blood is withdrawn from an artery with a needle and syringe. The procedure may be uncomfortable, but it is quick. Pressure must be applied for a few minutes afterwards to prevent bleeding.

Pulse oximeter

A machine called a pulse oximeter shines a light through the soft tissues of the finger or earlobe to measure oxygen levels in the blood painlessly.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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