Monitoring your blood oxygen levels is one of the most crucial things to do during a Covid infection, and could help determine if you need medical attention. While a pulse oximeter is the go-to device for checking your blood oxygen levels at home, you may also find a number of modern smartwatches these days that offer a built-in SpO2 sensor, also claiming to offer the same capabilities, along with the added perks of smartwatches.
However, does that mean that the new wearable you’ve been eyeing is as good as an oximeter? Dr Zakia Khan, Senior Consultant-Interventional Cardiology at Fortis Hospital, Kalyan, suggests otherwise.
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Khan explains that conventional pulse oximeters are more accurate than SpO2 smartwatches. While a smartwatch or fitness band may do the same job as a pulse oximeter, users can often expect a difference in readings owing to variations in accuracy.
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This difference can arise from how the two devices actually measure your oxygen levels. As Khan explains, “smartwatches use reflectance oximetry and oximeters use transmittance oximetry.”
What is transmittance and reflectance oximetry?
Transmittance and reflectance oximetry are two commonly used non-invasive methods to measure blood oxygen. They both use two light sources (infrared and red light) and a photodetector. The difference in working is based on the positioning of the components.
In transmittance oximetry, the light sources and photodetector are opposite to each other, while the site being tested (in the case of a pulse oximeter, your index finger) lies in the middle. When light passes through the target site, the photodetector on the other end measures the light that has passed through your finger to get a stable and accurate blood oxygen level reading.
However, due to their working, transmittance oximetry is most effective in a thinner measurement site, like your finger.
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In reflectance oximetry, the light sources and the photodetector are positioned on the same side, and the diode captures light reflected off the target measurement site (in the case of a smartwatch, your wrist). The light that reflects from the underlying bone is then detected by the diode, which takes a reading. The reason reflectance oximetry is often used in smartwatches and fitness trackers is because it does not require a thin site for measurement.
Why you should pick a pulse oximeter for accurate readings
Fingertip pulse oximeters are also equipped to compensate for external factors like ambient light, size of the finger and the light absorbed by tissue in your finger. Khan also points out that “pulse oximeters are more accurate because they have dual sensors,” something all smartwatches may not come with.
“Pulse oximeters are also more affordable,” Khan points out, making them much more accessible to people who may not be able to afford a smartwatch. While many pulse oximeters are priced below Rs 2,000, a SpO2-enabled smartwatch can cost anywhere between Rs 3,000 to Rs 50,000, and still may not be able to give you the same reliability in readings.
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Buyers can also invest in pulse oximeters that also give readings in a waveform, which Khan says are often superior to oximeters that only offer numeric data.
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What about when you cannot find an oximeter?
If you find yourself unable to buy an oximeter due to market scarcity, as was observed during the second Covid wave in various regions last year, then you can use a SpO2 smartwatch, says Khan.
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However, keep in mind that smartwatches are more suited for fitness-oriented use cases and not medical use. Further, all smartwatches that offer SpO2 sensors may not always give you the same reading. Khan points out that the sensors used by Apple in its wearables are better than other smartwatches. But then it is not the most affordable option in the Indian market.
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Khan further adds that having a pulse oximeter at home, along with a digital blood pressure monitor and a blood sugar monitor is a must during these times. These devices can be crucial when you need to monitor your vitals quickly. They are also easy-to-use and Khan suggests a quick search on YouTube can help users out with various kinds of pulse oximeters and other health monitors and how to use them.
