Study finds flaws in Apple Watch SpO2 sensor accuracy

Apr 24, 2023

A new medical study has called the Apple Watch blood oxygen saturation sensor's accuracy into question. When compared to conventional pulse oximetry, the readings are simply not adequate for clinical use.

The market has been flooded with new consumer-oriented health devices in recent years. One of these is the Apple Watch. It packs a plethora of health and fitness tech, user-friendly features, and seamless integration with other Apple products. This makes it a convenient solution for monitoring various aspects of personal health and wellness.

The oxygen saturation sensor on the watch has received a lot of attention. In recent years, blood oxygen saturation measurements from such devices have grown in popularity. There's no question about it. Something sitting on your wrist provides a more convenient and accessible alternative to traditional methods for capturing these types of measurements.

But how reliable are blood oxygen readings captured with these types of devices? A recent study was conducted to determine whether the Apple Watch's SpO2 sensor is good enough meet clinical use requirements.

The research was carried out by scientists from the Leipzig Heart Center's Department of Pediatric Cardiology. This was a single-arm, prospective study that compared the accuracy of oxygen saturation measurements taken with the Apple Watch 6 to the conventional method of pulse oximetry in patients with congenital heart disease.

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The study enrolled more than 500 willing participants. Following informed consent, routine oxygen saturation measurements were taken with a pulse oximeter, and three measurements were taken simultaneously with the Apple Watch. The findings revealed a statistically significant difference in measurement success between children and adults. Children had a higher proportion of unsuccessful measurements.

It turns out, how the watch was strapped around the person's wrist had a significant impact on the accuracy of the measurement. Strapping the watch properly improved the measurement over simply laying the watch on the wrist. However, while the cause of the high proportion of failed measurements in children can be attributed to movement, the cause in adults is unknown.

The findings show that the Apple Watch and other similar devices’ oxygen saturation measurements are not yet up to the medical standard of pulse oximetry. A large percentage of the measurements are still unsuccessful or incorrect.

So, while the readings are probably fine to use as a broad indicator of your SpO2, don't put too much stock in them. Smartwatches are still not as accurate as traditional methods of determining oxygen saturation. A traditional finger-tip blood pressure measuring device is likely to be more accurate.

Pulse oximeters measure blood oxygen saturation levels by shining a light through the fingertip, allowing for a more direct measurement of blood oxygen levels. Smartwatches, on the other hand, typically measure blood oxygen saturation levels using photoplethysmography (PPG), a less direct method that involves measuring changes in blood flow and light reflection in the wrist. Hence, the better accuracy of fingertip devices.

Source: Pätz, C., Michaelis, A., Markel, F. et al. Accuracy of the Apple Watch Oxygen Saturation Measurement in Adults and Children with Congenital Heart Disease.Pediatr Cardiol 44, 333–343 (2023). https://doi.org/10.1007/s00246-022-02987-w

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