Apple released Blood Oxygen (SpO2) monitoring capability on the Apple Watch Series 6, and it is now featured on most of its latest models.
Apple joins other players such as Fitbit, Garmin, and Samsung in offering the blood oxygen level monitoring feature via an on-wrist wearable device.
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Related:
- Is the Blood Oxygen app (SpO2) not working on your Apple Watch? Let’s fix it
- Amazfit adds new features for Stress and SpO2 readings to its app
- Does Fitbit, Garmin, or other wearable devices offer a Pulse Oximeter?
- New Study shows the efficacy of SpO2 readings on the Apple Watch
About Apple’s blood oxygen app for Apple Watch
It is important to note that the Blood Oxygen app measurements are not intended for medical use, including self-diagnosis or consultation with a doctor, and are only designed for general fitness and wellness purposes.
This same rule applies to all smartwatch manufacturers.
Unlike the ECG app that the FDA validated and Apple conducted numerous studies, blood oxygen level monitoring is relatively new and has not been put through a stringent FDA evaluation.
Apple Watch Series 6+ and Blood Oxygen Level monitoring
Apple Watch Series 6+ incorporates a new health sensor that helps with blood oxygen level monitoring. This allows for on-demand readings of your blood oxygen as well as background readings, day and night.
Given that the electrical heart sensor on Apple Watch Series 5 was pretty far more advanced than any other wearable out there on the market, one wonders why Apple needed to develop and use a new health sensor for the Apple Watch Series 6, just to introduce blood oxygen level monitoring
The new blood oxygen sensor is made up of four LED clusters and four photodiodes.
Incorporated into the completely redesigned back crystal, this new sensor works in concert with the Blood Oxygen app to determine your blood oxygen level.
It is possible that the new sensor will bring in additional bells and whistles pertaining to overcoming existing limitations to ECG measurement or dramatically improved accuracy for SpO2 monitoring.
If Apple had desired to just use basic heart rate and pulse-based calculations, it could have very well incorporated the SpO2 monitoring in its other watch models.
After all, you can find a smartwatch for less than $50 today on Amazon that offers SpO2 functionality via a regular optical heart sensor.
Blood oxygen readings on Apple Watch are not as accurate as medical devices 
Since most wearables that use light to detect heartbeat information tend to ‘calculate’ blood oxygen levels, it’s difficult to ascertain which manufacturer’s algorithms are more accurate.
Apple Watch does have a higher sampling rate than the other smartwatches when it comes to sensor technology. And recent studies indicate that Apple is doing a pretty good job with its SPo2 measurements: New Study shows the efficacy of SpO2 readings on the Apple Watch.
Clinical studies using Apple’s Blood Oxygen app & heart rate monitoring
Apple has tied up with the University of Irvine, California, to research how SpO2 and heart rate monitoring can be used effectively to help patients suffering from Asthma.
The company is also using the new Apple Watch with the University of Toronto to facilitate a study focused on understanding Heart Failure.
Samsung, Withings, and others offer SpO2 and other advanced blood monitoring features 
Samsung Galaxy Watch 3 and above also features an on-demand SpO2 measurement that can track how well your heart is pumping oxygen through the body while real-time feedback on VO2 max, the maximum amount of oxygen consumption, evaluates overall endurance during training.
Unlike Apple Watch, the new Samsung watch 3+ also provides users with a mechanism to measure blood pressure.
Withings Scanwatch also allows users to perform an on-demand SpO2 assessment to determine blood oxygen saturation levels.
ScanWatch uses a multi-wavelength sensor called PPG (photoplethysmography) sensor that emits and measures red and infrared reflections on the blood vessels in the wrist.
A SpO2 value is represented by a percentage. Normal SpO2 values vary between 90 and 100%.
The SpO2 readings also serve as a key input for Sleep Apnea detection on the Withings ScanWatch.
Garmin’s Vivosmart 4 and 5 fitness trackers also offer on-demand SpO2 tracking and can be relatively bought for $60 (refurbished), or a new one can be bought for $100.
Fitbit SpO2 monitoring via Fitbit
Fitbit’s Sense and Versa 2/3 smartwatches, along with their Luxe, Charge 4+ trackers also offer SpO2 monitoring. Fitbits use sensors to estimate your blood oxygen saturation (SpO2) only while you sleep.
The Fitbit Sense has some additional features too!
The Fitbit sense features a Biosensor core. Temperature, heart rate tracking, and SpO2 tracking all take place in this powerful, water-resistant (up to 50 meters) hub on the back of your Fitbit Sense.
The new biosensor core fuses glass and metal into a single, waterproof plate—an advanced process that’s used on aircraft and submarines.
This new Biosensor core on the Fitbit sense also helps with EDA Scan.
The on-wrist EDA Scan app detects electrodermal activity—which may indicate your body’s response to stress—and reveals a graph in the Fitbit app to illuminate it. This is another health feature that is not available yet on the new Apple Watch Series 6.
Older Fitbit smartwatches such as Versa and ionic models also offer SpO2 monitoring.
The key difference is that the Fitbit products track your SpO2 when you are sleeping. With the SpO2 clock face, your Fitbit Sense will track your average SpO2 levels while you’re sleeping. 
The older Fitbit devices do not have an on-demand Spo2 monitoring feature. Instead, it features EOV (Estimated Oxygen variation) which estimates changes in blood oxygen saturation levels.
Since the Apple Watch Series 6 just unveiled, it is hard to obtain the details around the new health sensor on the Apple Watch Series 6. We will update this post as new details are unveiled.
Key shortcomings of wrist-based Pulse Oximetry 
There are some shortcomings with the way SpO2 is monitored today via pulse oximeters and smartwatches. It is probably the main reason why the feature has not been evaluated and validated by FDA for any smartwatch maker.
Here are some situations when the SpO2 monitoring via your smartwatch can fall short.
In order to judge a patient’s condition, ideally, you would like to have blood oxygen saturation expressed as a percentage of the total hemoglobin that is saturated with oxygen.
Under many circumstances, that is the reading you get from pulse oximeters. However, if the patient has a large amount of non- functional hemoglobin, the reading is not accurate.
Several situations can lead to such large amounts of non-functioning hemoglobin. Carbon monoxide poisoning and even heavy smoking increase the amount of carboxyhemoglobin, non-functioning hemoglobin.
So if you are a heavy smoker, chances are that your SpO2 readings obtained via any of these leading smartwatches may not be correct.
The same holds for users who suffer from Anemia. Damage to red blood cells may cause anemia, a lack of red blood cells, and thus hemoglobin in the blood.
An anemic patient may not have enough functioning hemoglobin in the blood to oxygenate the tissues.
The small amount of functioning hemoglobin in the blood may be well saturated with oxygen, so the patient may have a normal SpO2 reading, but the patient may not have enough oxygen going to the tissues.
The human body reduces the heat lost by the skin by constricting the peripheral blood vessels. So if you are performing an on-demand SpO2 reading in colder temperatures, you will have to account for the inaccuracy in the readings.
Summary
If you are looking for a Smartwatch that offers ON-DEMAND blood oxygen saturation level monitoring, your choices are the Samsung Galaxy Watch 3, Apple Watch Series 6, Withings ScanWatch, and the Garmin products.
If you are looking for a Smartwatch that provides excellent quality of health monitoring with ECG features, sleep tracking, stress tracking, heart zone monitoring, and required SpO2 monitoring, the Fitbit Sense with its Pulse 2.0 technology is a decent product to consider.
Here at myHealthyApple, we think that the Apple Watch Series 6 is the way to go forward!
As more and more health studies are performed, we will get to understand the accuracy of these smartwatches when it comes to monitoring blood oxygen saturation levels.
