Doctors can measure blood oxygen levels using an arterial blood gas, or ABG, test, which requires a blood sample taken from an artery, explains WebMD. Another option is a pulse oximeter, notes Mayo Clinic. The device measures blood oxygen saturation, which can serve as an estimation of blood oxygen levels.
Most blood tests use blood drawn from veins, but an ABG test requires arterial blood because it enables the doctor to measure oxygen and carbon dioxide levels before they have a chance to enter bodily tissues, states WebMD. The test also provides a measure of the blood's pH, or acidity, level.
An ABG test can be used to diagnose hypoxemia, a condition in which there is an insufficient amount of oxygen circulating through the blood and into the tissues and cells, notes Mayo Clinic. Patients with hypoxemia may present with shortness of breath due to the lack of oxygen. Doctors may also perform ABG tests if a lung disease or major breathing problem, such as asthma or cystic fibrosis, is suspected, according to WebMD. In patients with diagnosed lung diseases, an ABG test can help gauge how well the treatment is working. Another use for the test is to make sure hospital patients receiving supplemental oxygen are getting the proper amount.