In order to determine whether you have hypoxemia, your doctor will need to check the amount of oxygen in your blood. Most often, your doctor will use an oxygen monitor that is placed on your finger. However, sometimes your doctor will take a blood sample to measure oxygen levels in the blood.
If the cause of your hypoxemia is unclear, your doctor may perform lung function tests. These tests measure how much air you can breathe in and out, how fast you can breathe out, and how well your lungs deliver oxygen to the blood. The most common lung function test is called spirometry and measures how much air you can breathe out after taking a deep breath and how fast you can expel the air.