Apple Watch Series 6: SpO2 tracking is still in its early stages


The Apple Watch Series 6 feels like it has perfected many of the features I liked about its predecessor. It has a brighter always-on display, a more powerful processor, faster charging and two new colorful options to choose from. But the feature I was most excited to try out was its new sensor that measures oxygen saturation in the blood (aka SpO2) with the tap of a screen. As someone who panic-bought a pulse oximeter at the start of the coronavirus pandemic and still checks her levels at the first sign of a cough, the thought of having one strapped to my wrist at all times was enough to pique my interest.

But unlike the ECG feature on the Apple Watch, which has been tried, tested and cleared by the US Food and Drug Administration, along with the irregular heart rhythm notifications, SpO2 on the Apple Watch still seems to be in its early stages. Navigating all this new data can be daunting for anyone who’s not a medical professional.

SpO2 leaves some unanswered questions

I bought an FDA-cleared pulse oximeter, the device doctors use to measure SpO2 on your fingertip, as a precaution when coronavirus cases in the US started to climb. Having low blood oxygen levels doesn’t guarantee you have COVID-19, but it’s one of the major symptoms of the disease. I had read horror stories of people who waited too long to go to the hospital and had died in their sleep because they didn’t realize their levels had dipped overnight. You should always check with a physician if you are experiencing shortness of breath (another symptom of COVID-19), even if a pulse oximeter says you’re in a healthy range, but I found comfort in knowing that I could at least use it as a reference if I ever experienced shortness of breath.

That’s not something you can do with the Apple Watch — Apple says it should be used for wellness purposes only and not as a medical device, meaning you’ll have to take the results with a grain of salt and shouldn’t use it to screen for any type of disease, which is what I had been hoping to get out of it. But there may be other advantages of having it strapped on your wrist at all times.


Much like a pulse oximeter, the Series 6 uses red and infrared light from its new sensor to determine the percentage of oxygen in the blood. But instead of shining the light through your fingertip, it uses the light that’s reflected back from the blood vessels in your wrist to determine your oxygen levels based on the color of your blood.

During the setup process you’re asked whether or not you want to activate SpO2 tracking, which I did, but you can always go back and disable it in the settings after the fact. The first thing I did after strapping on the Watch was open the Blood Oxygen app. It gives you a few tips on how to get the best result and you need to rest your arm on a table or flat surface while the Watch is taking a reading. Then the 15-second countdown begins and you’re done — straightforward and painless. I got a 95% on my first read, which was lower than what I’m used to from my pulse oximeter. Anything above 90% is generally considered by clinicians to be within a healthy range, but in most cases, higher is better.

I tested it a few more times and got slightly different results within a few percentage points depending on whether I was completely still and silent during the test, where I had the watch positioned on my wrist and how tight the strap was. There are many factors that can affect a reading, such as skin temperature or the position of the sensors on the body. Side-by-side with my pulse oximeter, the Apple Watch was often off by about one or two points, but sometimes spot on.

Measuring blood oxygen levels over time

What was more interesting to me was the SpO2 data that collected over time in the Health app. That’s something my pulse oximeter can’t do. Unlike the Galaxy Watch 3, which only does spot checks, the Apple Watch also takes background measurements throughout the day (and night). Click on the Respiratory option on the dashboard and you’ll see all your measurements plotted on a graph which you can view a day, week or month at a time and filter by time of day or percentage. But it’s up to you, or ideally your physician, to interpret this data…Read more>>



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