Should You Trust the SpO2 Monitor on Your Smartwatch/Smart Band, or Buy a New Oximeter Instead?

The SpO2 monitor has become increasingly common on most smartwatches after the Covid-19 pandemic, as have demands for pulse oximeters.

With the outbreak of the severe, double mutation strain, the Covid-19 pandemic has taken a grave turn in India. With hospitals beds, oxygen supplies and key medical supplies running scarce, more and more individuals are repeatedly being urged to stay at home, and apply for the Covid-19 vaccination process at the earliest. In all of this, one key instrument that has come to the fore is the pulse oximeter, a pathological instrument that until the turn of the pandemic was never particularly a household name. With this, a new smartwatch feature also shot to popularity – the SpO2 sensor to monitor your blood oxygen levels. However, a closer look at either of the two instruments may suggest that the results produced by them are indicative at best – and far from clinical in accuracy.

How a smartwatch’s SpO2 monitor works

The key conversation to have here is to consider how accurate the SpO2 monitor available in smartwatches are, in reference to the standalone pulse oximeters being sold in the market. An SpO2 monitor aboard most smartwatches and fitness wearables typically use two LEDs – a standard red and an infrared. The need for varying wavelengths arise from how blood reacts to wavelengths of these incident lights – well oxygenated blood supply in the human body typically absorbs infrared light, which would mean that your blood oxygen levels are adequate.

This is critical to note, particularly in recent times, as pulmonary infections are the biggest target infections among Covid-19 patients. As a result, monitoring the blood oxygen levels have become crucial, which in turn are leading to more smartwatches, including super affordable ones, too, getting the feature. Add to the lack of availability of the standalone pulse oximeter due to very high demand in the market, and buying a smartwatch may just be your only choice.

The question is, can you trust this data, particularly from inexpensive smartwatches and trackers with onboard SpO2 sensors?

Comparative accuracy

There are two parts to this tale. Beginning with the small, inexpensive clip-on pulse oximeters, they themselves have often been regarded as not highly accurate. In other words, it clearly has its own irregularities. In a medical validation study conducted by pioneering research Gunther Eysenbach, and including practising doctors such as Geno J Merli, director of the Jefferson Vascular Centre in Philadelphia, USA, there is discrepancy even in portable physiological measurement devices.

The research study then goes on to label its sample smartwatch as “not accurate enough to be used as a vital sign’s measurement device.” It further adds, “The (device) was substantially more accurate, but it still failed to meet predefined accuracy guidelines for SBP and SpO2. The continued sale of consumer physiological monitor devices without the required prior validation and market approval procedures is a significant public health concern.” For reference, the study used a clip-on health stat tricorder that ranks as one of the more expensive and accurate monitors of health parameters in comparison to mainstream pulse oximeters.

In an interview with Wired, Joao Paulo Cunha, associate professor at the department of computer and electrical engineering, University of Porto said, “(The inaccuracy) is because these sensors are not precise, that’s the main limitation, even the heart-rate monitors are not very precise. 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. Some of the companies, for example Fitbit knows it would be lying to customers if it puts out the values and says ‘use these values’ so that’s why they’re not doing it.”

Can you rely on this at all?

Anyone using a fitness wearable will certainly vouch that recorded data of SpO2 measurements are, at the very least, inconsistent. It also requires users to stay steady and still during the measurement period, and even then, some of the cheapest wearables fail to take readings. Such devices are surely not to be taken with legitimacy when it comes to blood oxygen recordings. In case of a pulse oximeter, even though they are not entirely accurate, the general reading consistency levels are better than this.

Given that general research and expert opinion clearly highlights the inconsistency of smartwatch SpO2 readings, and medical bodies have also shied away from certifying even the best smartwatches such as the Apple Watch, there’s no denying that making a rushed purchase of a wearable tracker does not make complete sense. It may serve as a general indicator, and will seem like a better investment in terms of the entire feature set, but you are better off inquiring with your local pharmacy or smaller vendors and getting your hands on a dedicated finger clip-on pulse oximeter.

If you already have a smartwatch that supports SpO2 measurements, use it only as an approximate and unofficial safeguard against potential oxygen drops. Check to ensure that the blood oxygen levels stay at 95 percent and above, and for constant readings at 90 percent or below, consult a doctor at the earliest.

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