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Should you use oximeters or smartwatches for COVID-19 SpO2 readings? Doctors answer

There are many factors and scientific reasons that determine the accuracy of the smartwatches and the oximeters. But let's hear what the doctors have to say.

UPDATED: May 12, 2021 15:05 IST

A friend I know bought a smartwatch when he started experiencing symptoms of COVID-19, primarily to keep a check on his blood oxygen levels. When asked why he bought a device worth Rs 30,000 instead of an oximeter which costs a fraction of the smartwatch. He said he trusts the smartwatch more than the oximeter because it costs more. While there is absolutely no logic to what he said, the dilemma to use an expensive smartwatch over an oximeter has been faced by many.

Oximeters have become scarce ever since the COVID-19 cases have surged in India. Most chemist shops have run out of stock while some are selling them at exorbitant prices. The e-commerce platforms don’t have very many options to choose from.

The first thing that the doctor wants to know about is your saturation level when you seek treatment for COVID. “How much is your blood oxygen level?”, you are often asked because your score determines your condition. It decides whether you should be hospitalised or isolate at home. Well, you can certainly do without ivermectins, azithromycins but not without a device that monitors your blood oxygen levels.

But what if you don’t have an oximeter, should you trust the readings displayed by your smartwatch or wait till the oximeter arrives? There are many factors and scientific reasons that determine the accuracy of the smartwatches and the oximeters. The difference is mostly due to reflectance oximetry and transmittance oximetry. The smartwatches use reflectance oximetry while the oximeters use transmittance oximetry.

But let’s hear what the doctors have to say about the two technologies and which one is more reliable than the other.

How accurate are oximeters?

Dr Ajay Mohan, a surgeon from AIIMS Delhi, explained the technology that is used by oximeters to measure blood oxygen levels. “The pulse oximeter uses an electronic processor and a pair of small light-emitting diodes (LEDs) facing a photodiode through a translucent part of patient’s body (fingertip or earlobe). One LED is red, with a wavelength of around 650 nanometers, and the other is infrared with a wavelength of around 950 nanometers. Absorption of light at these wavelengths differ significantly between oxygenated blood and non-oxygenated blood. Oxygenated blood absorbs more infrared light and allows more red light to pass through. Deoxygenated blood allows more infrared light to pass through and absorbs more red light. This difference is calculated by the receptor and the calculated SpO2 value is being displayed on the monitor,” he told India Today Tech.

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Mohan explained that the accuracy of pulse oximeters is highest when the saturation level is above 90 per cent but its accuracy dims when the saturation is below 80 per cent. He noted that the accuracy of smartwatches is much less compared to the oximeter but when it comes to measuring heartbeats, both the devices are at par with each other. Mohan suggested that even a cheaper oximeter is far more accurate than an expensive smartwatch. However, he did mention that smartwatches can be used to get a rough idea about the SpO2 if there is no oximeter available.

What about the accuracy of smartwatches?

Dr Deepak Aggarwal, Senior Consultant, Cardiac Surgery, Max Super Specialty Hospital, Saket told India Today Tech that most oximeters have an upper hand over the smartwatches, but they too have their flaws like any other electronic devices. It also has got a lot to do with how you place your finger. “The oximeters need to be placed properly. If flow at the placed finger is not good you will have incorrect readings. In case, saturation is below 70% they will show erroneous results.”

Talking about the smartwatches, Dr Aggarwal said that the smartwatches are not as accurate enough to be used as a vital sign’s measurement device, they are good for consumer-level but should not be used for clinical purposes.

“The (device) was substantially more accurate, but it still failed to meet predefined accuracy guidelines for SBP and SpO2. They have to be well-calibrated. The inaccuracy is because these sensors are not precise, that’s the main limitation. So, the ones that you wear are only for the consumer level, not for the clinical level. Pulse oximetry is another level of detail and precision that you need so that you have a usable value.”

Accuracy can be an issue in smartwatches and oximeters as well

Dr Deepak Krishnamurthy, Senior Interventional Cardiologist at a hospital in Bangalore told us that both the oximeters and smartwatches can be fairly accurate, but it is important to check and calibrate in a doctor’s office to confirm the accuracy.

“Some spurious oximeter brands have now come into the market, and they can be inaccurate. It is important to check and calibrate and compare once in a doctor’s office if it is working properly. Apart from that because of so many brands available it is really difficult to say which one is good. Accuracy can be a significant issue in these times because we advise Covid patients to stay at home or get admitted based on oximeter readings. The health authorities should have quality control on these commercially available oximeter brands and provide some sort of certification,” he told India TodayTech.He noted that the accuracy of smartwatches also depends on how well-calibrated the device is. Smartwatches need certification across brands.

What are smartwatch companies doing to improve accuracy?

There are just too many smart bands in the market to choose from and each comes with a SpO2 monitor. They come in different price tags, shapes and sizes, but none has reached the level accuracy of that is expected from a medical-grade device. So are smartwatch companies working to improve their SpO2 tracker because that is the only feature that is needed right now?

Amazfit, which is a popular fitness wearables brand in India, had compared their Spo2 tracker with a professional oxygen analyser to check the accuracy.

“The company has invested hugely in R&D and developed a platform of proprietary technology including AI chip. Compared with the results of professional oxygen analyzers, the average error of OxygenBeats is only 1.67% reflecting accuracy superior to that of most wearable wrist devices for blood oxygen detection. Smartwatch Spo2 readings are indicative measures to be accurate but should not be considered an alternative to medical-grade devices. Our team has also collaborated with medical institutions and R&D centres for the smart wearable joint laboratory to combat COVID-19 using data from our AI platform,” Honey Singh, brand advisor, told India Today Tech.

We spoke to Vishal Gondal, Founder and CEO, of Made-In-India wearables brand, GOQii about how smartwatches companies are working towards making their features better and accurate. He told that some of GOQII smartwatches have received medical device registration under the Ministry of Health and Family Welfare, which is the national regulatory body for Indian pharmaceuticals and medical devices.

“We have been conducting studies with various organisations on the use of advanced wearable technology to be able to provide the medical fraternity with detailed health data of patients under their care real-time. The initial response from the fraternity has been positive and a lot of emphases is being laid upon the accuracy of the data,” Gondal said.

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