Teach Me

What You Need to Know About Your Blood Oxygen Level

Before 2020, you probably didn’t think much about your blood oxygen levels. Maybe there was a time you got sick or needed surgery, and a health professional clipped a sensor to your fingertip to test your levels. It’s likely you haven’t thought about those measurements since then.

Until this year, that is. COVID-19 has shown us how our lung health and oxygen levels are interconnected. And manufacturers of some of the latest fitness trackers are adding features that can measure levels of oxygen in your blood. Here’s what you need to know.

What does my blood oxygen level tell me?

Your blood oxygen level measures how much oxygen is circulating with your red blood cells. You can measure your blood oxygen level with a pulse oximeter. That’s a small device that clips onto your fingertip. It shines a light into the tiny blood vessels in your finger and measures the oxygen from the light that’s reflected back.

Your blood oxygen level is measured as a percentage—95 to 100% is considered normal.

“If oxygen levels are below 88%, that is a cause for concern,” said Christian Bime, MD, a critical care medicine specialist with a focus in pulmonology at Banner - University Medical Center Tucson. If you see readings at or below this level, you should seek medical attention. Contact your health care provider immediately or go to the nearest urgent care center or emergency room.

How does COVID-19 affect blood oxygen levels?

Some people with COVID-19 have dangerously low levels of oxygen. If you’ve been exposed to COVID-19, or you’ve tested positive but don’t have symptoms, there’s no need to check your blood oxygen level, Dr. Bime said. But if you develop symptoms, like feeling short of breath or are having trouble breathing, you might want to check your level. If it’s low or you notice it’s dropping, contact your health care provider.

Are there other times I should be checking my blood oxygen levels?

If you have chronic lung disease or heart conditions, your doctor might want you to routinely check your blood oxygen levels using a pulse oximeter at home. Dr. Bime said it’s recommended for people with:

  • Chronic obstructive pulmonary disease (COPD)
  • Congestive heart failure
  • Pulmonary fibrosis
  • Pulmonary hypertension
  • Asthma
  • Cystic fibrosis

What causes low blood oxygen levels?

Different situations can cause low oxygen levels:

  • Pus, blood, or water filling the air sacs in the lungs
  • Blood clots in the lung
  • Scarring or loss of lung tissue
  • Sudden exercise, if you have heart or lung disease
  • Not breathing, in someone who is profoundly intoxicated, for example
  • Transitioning from low altitude, where the air has a high concentration of oxygen, to high altitude, where there’s a low oxygen concentration.

How can I check my blood oxygen level?

You have a few options. You can buy an FDA-approved pulse oximeter from a pharmacy or online retailer for $15 to $30. Dr. Bime recommends them for many of his patients with chronic diseases. He suggests people bring the devices to their doctor’s appointments to compare measurements.

Some of the latest wearable fitness devices can also measure your blood oxygen level—the Apple Watch Series 6, 7 and 8, Samsung Galaxy Watch 3 and 4 and certain Fitbit and Garmin devices track it through your wrist, and the Wellue Continuous Ring Oximeter takes readings from your finger.

They can be okay, with caveats. “There is a lot of variability in how these devices measure the oxygen levels, and these methods have not been cleared by the FDA,” Dr. Bime said. “As long as you compared the results to those from an FDA-approved device, they are fine.”

If you notice low oxygen levels on a fitness tracker, contact your health care provider for an evaluation. If your wearable device shows a normal oxygen level, but you don’t feel well, Dr. Bime still recommends getting evaluated by your doctor. “Do not be falsely reassured,” he said.

Related articles:

Heart Health Hypertension Pulmonology and Asthma COVID-19