How to take a Blood Oxygen reading on Apple Watch

Apple Watch Series 6 introduce a new sensor system that enables you to measure oxygen saturation in your blood, which should help you keep a better watch over your own health. How does it work?

What’s the technology?

The new sensor works with Apple’s own software to assess your blood oxygen levels.

In practise, it achieves this using four clusters of green, red, and infrared LEDs, along with the four photodiodes on the back crystal of Apple Watch, shining red and infrared LED lights into your skin to find the blood vessels in your wrist.

The photodiodes then assess the light reflected from your wrist during this operation to estimate blood oxygen levels.

Is this accurate?

Apple isn’t telling us it’s accurate enough for medical diagnosis. Instead is describes the tool as a useful way to monitor your own health.

What is also interesting about blood oxygen levels is that they can be used to detect the early warning signs of COVID-19, and there are researchers looking into how accurately Apple Watch can determine this, the company said.

It is engaging in three studies to explore the application of the tech for the following important areas:

• To see if it can provide early warning of COVID-19 and flu.
• To manage and control asthma.
• To help manage heart failure.

What is normal?

Normal blood oxygen rating is between 95% and 100%. Anything below that could signal some form of medical emergency, says the WHO.

How to take a Blood Oxygen reading on Apple Watch

It’s very easy to take the measurement if using an Apple Watch Series 6 which hosts the sensor. Older Apple Watch models do not have this sensor.

• Press the Digital Crown
• Launch the app screen
• Tap the Blood Oxygen app icon, (a red and blue circle).
• You can also ask Siri to open the app for you.
• Press Start and you will see a 15-second countdown appear on-screen while it takes a reading.

You will then be presented with your blood oxygen levels and this information will be shared with the Health app so made available to other systems on your device so long as you choose to do that.

On-demand measurements can be taken while the user is still, and periodic background measurements occur when they are inactive, including during sleep.

What Apple said

In the 2020 press release in which it introduced its new tool, Apple said:

“Apple Watch Series 6 expands the health capabilities of previous Apple Watch models with a new feature that conveniently measures the oxygen saturation of the user’s blood, so they can better understand their overall fitness and wellness. Oxygen saturation, or SpO2, represents the percentage of oxygen being carried by red blood cells from the lungs to the rest of the body, and indicates how well this oxygenated blood is being delivered throughout the body.

“To compensate for natural variations in the skin and improve accuracy, the Blood Oxygen sensor employs four clusters of green, red, and infrared LEDs, along with the four photodiodes on the back crystal of Apple Watch, to measure light reflected back from blood. Apple Watch then uses an advanced custom algorithm built into the Blood Oxygen app, which is designed to measure blood oxygen between 70 percent and 100 percent. On-demand measurements can be taken while the user is still, and periodic background measurements occur when they are inactive, including during sleep. All data will be visible in the Health app, and the user will be able to track trends over time to see how their blood oxygen level changes.”

Stay safe out there.

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