Oxygen saturation in arterial blood measured from arterial blood gas (PO₂)

Why This Test Is Done

Doctors may order this test if you have symptoms like shortness of breath, fatigue, or confusion, especially after conditions like pneumonia, asthma, or heart problems. It’s also used during surgeries, anesthesia, or if you have chronic lung diseases like COPD. Sometimes, it’s part of a broader blood gas evaluation to check how well your body is processing oxygen.

How the Test Works

A small sample of your blood is taken from an artery (usually in your arm) and analyzed in a lab. The test measures the percentage of oxygen molecules bound to hemoglobin in your red blood cells, which is represented as a percentage (saturation). The PO₂ value indicates the partial pressure of oxygen in your blood, which can help correlate with oxygen saturation levels.

What to Expect Before the Test

You’ll likely have a small needle inserted into your arm or wrist to draw blood. It may feel like a quick pinch, and you might feel a brief sting. If you’re having surgery or a procedure, the doctor may explain how the test fits into your care plan. Avoid eating or drinking for a short time before if instructed.

What to Expect During the Test

The blood sample is sent to a lab where it’s analyzed immediately or within minutes. Results are usually available within a few hours. If you’re undergoing continuous monitoring (like in the ICU), results may be real-time.