A smart watch measures the oxygen in the blood for years. But is it useful?

Smart watch it can measure everything from heart rate to sleep quality, but one health metric has become particularly relevant in the last two years: blood oxygen saturation. Two of the world’s largest smart watch manufacturers, Apple and Samsungthey added blood oxygen monitoring to their wearable devices in 2020. The COVID-19 pandemic also made measuring vital signs from home more desirable.

But the advent of blood oxygen monitoring in smart watches has also raised questions about how useful this information is without the context of a medical professional. In CNET reviews Apple Watch Series 6Vanessa Hand Orellana said she would like the Apple Watch to provide more guidance for accompanying blood oxygen measurements. (When her level dropped to 92% overnight, she didn’t know if she should be concerned.) Most smart watches are also not approved by the U.S. Food and Drug Administration for blood oxygen measurement and cannot be used for medical purposes. it is difficult to understand how these metrics should be interpreted.

About two years later, are blood oxygen measurements more useful than in 2020? The answer is not that simple. Medical experts say that measuring blood oxygen during the day and under different conditions can unlock knowledge that you will not gain with a traditional pulse oximeter. In addition, having more access to health data from home is also usually a good thing.

But these sensors still have shortcomings that can limit usability. And smart watch manufacturers are still looking for the best ways to incorporate blood oxygen measurements into broader features that give users a complete picture of their overall health.

“We know that the science behind them is still not as accurate as that at the hospital level in terms of how oxygen is determined,” said Dr. Albert Rizzo, chief physician of the American Lung Association. “But when I said that, they became useful in terms of patients, or even people who are sick, even healthy people, to be able to monitor other vital signs.”

Breakthrough in blood oxygen monitoring

To understand whether measuring blood oxygen levels from your smartwatch is useful, it is important to first know what this metric means and how it is implemented in today’s wearable devices. Yours blood oxygen levels, also known as SpO2, indicates how much oxygen your red blood cells carry. It is considered an important indicator of respiratory health because it signals how well your body is able to absorb oxygen.

Blood oxygen saturation is usually measured through pulse oximeter which attaches to your finger. Smart watches like the Apple Watch measure this by shining a light on your wrist and measuring the reflected light.

If your current smart watch or fitness tracker can’t measure your blood oxygen level, chances are it will be the next one you buy. This technology has become the basis of today’s wearable devices and can be found in products from Apple, Samsung, FitbitGarmin and Withings, among others.

The Apple Watch Series 6 and Series 7 both measure the oxygen level in the blood, just like the Samsung Galaxy Watch 3 and Watch 4. Fitbit devices such as its Sense, Ionic and Versa smart watches and Charge 4, Charge 5 and Luxe fitness bracelets can also measure blood oxygen levels overnight during sleep.

However, most companies have not obtained FDA approval for their blood oxygen measurement technology. Withings is an exception; monitor blood oxygen in your ScanWatch and ScanWatch Horizon they are both FDA approved. Maxime Dumont, Withings’ smart watch product manager, says FDA approval should increase data credibility for physicians.

“We never replace a doctor and we do not intend to make any diagnosis with a watch,” he said. “But the results of the watch are reliable for doctors.”

Read more: Fitbit and Apple know that their smart watches are not medical devices. But you?

Although it was possible to read blood oxygen levels from smart watches before 2020, the technology had a breakthrough two years ago. As the pandemic gripped hospitals and the health care system, there was increasing interest in research into how wearable devices could monitor bodily changes at home.

Devices from Apple, Fitbit, Garmin, and Oura were all used in research to investigate whether wearable devices can predict disease in a timely manner by measuring changes in body signals such as heart rate and temperature. A 2021 study published in scientific reports by researchers from the University of Sao Paolo and the Centro Universitário FMABC also found that the Apple Watch Series 6 is reliable in collecting SpO2 and heart rate data in patients with lung disease in a controlled environment.

“The huge number of people the health care system has had to deal with has made it easier for health care systems to experiment with these non-clinical oxygen sensors,” said Dr. Nauman Mushtaq, Medical Director of Cardiology at Northwestern Medicine Central DuPage and Delnor Hospital.

How useful are these sensors in a smart watch?

While health sensors in smart watches are promising in research, some experts are unsure how often these sensors are used in everyday conditions. “I’ve had several patients who have used Apple Watch or similar devices to monitor their blood oxygen levels,” said Dr. Ashraf Fawzy, pulmonologist and critical care physician and assistant professor of medicine at Johns Hopkins University. “But it wasn’t as common as I thought.”

As for regular use, Dr. Mushtaq sees oxygen sensors in the blood in devices such as Apple Watch as most useful for adding another context related to overall health. In most cases, the average healthy person would experience physical warning signs of hypoxemia or low blood oxygen levels, he said.

“To be honest, I don’t think it’s doing something that’s clinically important to the average person,” he said.

This does not mean that medical professionals do not see the potential. Smart watches have a big advantage over traditional pulse oximeters: their position on your wrist all day long. In addition to random checks, many smart watches can measure blood oxygen in the background, which means they can collect data at different times of the day.

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Fitbit, Samsung, Garmin and Apple devices can passively monitor blood oxygen levels during sleep, unlike the traditional pulse oximeter used for on-demand measurements. Both Apple and Garmin can also take regular blood oxygen samples throughout the day.

However, a smart watch is only good for checking SpO2 levels at rest, even when scanning in the background. (Apple says that background measurements occur when the user is not moving, and Garmin says that they measure less often if it detects high motion).

According to Dr. Measuring Fawzy’s blood oxygen levels during strenuous activities would make these devices more useful, as it could help doctors determine whether to adjust the amount of oxygen prescribed to the patient. Dr. Mushtaq also said that patients with heart failure or pulmonary hypertension could benefit from a reduction in their blood oxygen levels during exercise.

“That can certainly help,” Dr. Fawzy said. “Because for some people, their oxygen levels only drop when they’re active, and they’ll be normal when they’re sitting quietly.”

Health metrics are most useful in context, whether it’s blood oxygen levels or how many steps you’ve taken. Numbers and graphs are only important if you know how to use them properly.

“In the end, consumers don’t buy sensors,” said Julie Ask, vice president and chief analyst at research firm Forrester, in a previous interview with CNET. “They don’t buy data. Consumers buy what they hope will help them get the result.”

So what context does a smart watch have to provide to make blood oxygen levels more useful? Some companies try to answer this question by combining SpO2 results with other features and wellness reports in the app to better understand your overall health. For example, Samsung is incorporating SpO2 metering into its own sleep coaching According to a Samsung representative, there is a feature on the Galaxy Watch 4 that will help you understand your sleep patterns. Withings uses blood oxygen levels as one of the metrics it analyzes when determining respiratory disorders, along with heart rate and exercise.

Phil McClendon, manager of Garmin’s wellness product management team, was unable to comment on future plans when asked if SpO2 measurements would be included in other health findings. However, he cited Garmin’s Health Snapshot as an example of the company’s approach to making health data more meaningful.

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Health Snapshot collects various metrics (including heart rate, blood oxygen, heart rate variability, respiration, and stress) to provide an overview of your cardiovascular status. McClendon said this feature helps people quantify the changes that can happen in their bodies during abnormal events.

“So maybe they have a panic attack and they say, ‘I want to upload and export a PDF to take them to my healthcare provider,'” he said as an example.

Right now, the biggest benefit of measuring blood oxygen levels is using a smart watch to find out what is considered normal for your body. Although smart watches are not intended for medical diagnostics, this is another signal you can take from your doctor if you do not feel well or notice physical changes.

“Whatever device you use, compare it to your baseline, use it as a trend monitor to let you know you’ve deviated from your baseline,” said Dr. Rizzo of the American Lung Association. “It may allow you to change what you’re doing or seek help before you do otherwise.”