Translation of a-t 2025; 56: 31

Warning - unreliable glucose measurements taken by smartwatches and the like

In France, warnings are currently being issued about devices such as smartwatches and smart rings that claim to be able to measure blood sugar levels through skin contact alone.¹ The US drug authority, the FDA, also issued a warning about products of this type last year and noted that no smartwatch or smart ring with a non-invasive measuring process that does not puncture the skin has been approved or authorised by the authority yet.² To test the alleged glucose measurement function, two smartwatches were purchased online from Germany for a pilot test.³ The watches are equipped with an optical sensor and claim to be able to determine oxygen saturation, heart rate, body temperature and blood pressure, in addition to blood sugar. A person with type 1 diabetes wore the two devices, one on each wrist, continuously throughout the day on two consecutive days. Conventional continuous glucose monitoring was also carried out. The glucose levels recorded by the smartwatches on the two days were almost identical, with rises at the times typical for main meals, although the peak levels on one watch were significantly higher than those on the other (160 mg/dL compared to 130 mg/dL). When the data were compared with the data from the conventional monitoring no clinically meaningful similarity was able to be identified. Even when the watches were attached to a banana on the third day, the glucose levels did not differ practically at all from those on the first two days.³ The devices thus proved to be entirely useless for measuring blood sugar, and even dangerous: the manufacturers of the two watches stated that they are not medical devices so they are not suitable for medical purposes,³ but diabetes patients could be tempted to focus on (apparently fictitious) values of this type and feel a false sense of safety, as indicated by a report ⁴ on a 60-year-old with type 2 diabetes who was shocked at her high HbA_1c (11.9%) at a check-up because her smartwatch had displayed normal blood sugar levels recently. A subsequent test showed a significant discrepancy between the values on the watch and the actual glucose levels (e.g. an average of 211 mg/dL with the continuous subcutaneous measurement compared to 92 mg/dL according to the watch).⁴ In the worst case, life-threatening hypoglycaemia or hyperglycaemia may not be noticed (in time) and/or incorrect doses of medication could be administered.^1,2 Healthcare professionals should therefore expressly warn against using devices of this type to monitor diabetes, –Ed.

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