What happens during a blood oxygen level test?
Most blood tests take a sample from a vein. For this test, a health care provider will take a sample of blood from an artery. That's because blood from an artery has higher oxygen levels than blood from a vein. The sample is usually taken from an artery inside the wrist. This is called the radial artery. Sometimes the sample is taken from an artery in the elbow or the groin. If a newborn is being tested, the sample may be taken from the baby's heel or umbilical cord.
During the procedure, your provider will insert a needle with a syringe into the artery. You may feel a sharp pain as the needle goes into the artery. Getting a blood sample from an artery is usually more painful than getting blood from a vein, a more common type of blood test procedure.
Once the syringe is filled with blood, your provider will put a bandage over the puncture site.  After the procedure, you or a provider will need to apply firm pressure to the site for 5–10 minutes, or even longer if you are taking a blood-thinning medicine.
