This is similar to a blood test but instead of a needle going into a vein it is inserted briefly into a small artery in your wrist.  A small amount of blood is taken and sent to the laboratory for information about the oxygenation of your blood and other gases.

Blood gas measurements may also be used if you have known respiratory, metabolic or kidney disease, especially if you have severe difficulty breathing. Many conditions can cause a blood gas imbalance and while the blood gas tests do not identify the exact cause of the imbalance they will point to either a respiratory or metabolic problem.

It is also used to assess the requirement for home oxygen in patients with very severe emphysema.