When Dan Heller obtained his first batch of Dexcom’s newest continuous glucose monitors in early 2023, he determined to run a small experiment: He wore the brand new biosensor and the earlier technology on the similar time to see how they in contrast in measuring his glucose ranges.
The brand new, seventh-generation mannequin (aptly referred to as the G7) made by San Diego-based healthcare firm Dexcom had simply begun delivery within the United States. Dexcom claimed the G7 to be the “most accurate sensor” out there to the hundreds of individuals with Sort 1 diabetes who use steady glucose monitors to assist handle their blood sugars. However Heller discovered that its real-world efficiency wasn’t as much as par. In a September 2023 put up on his Substack, which is devoted to protecting Sort 1 diabetes analysis and administration, he wrote about the experience and predicted a rise in adversarial occasions with the G7, drawing on his previous expertise main tech and biotech firms.
Within the two years since Heller’s experiment, many different customers have reported points with the machine. Some complaints regard failed connection and deployment points, which Dexcom claims to have now addressed. Extra regarding are reviews of erratic, inaccurate readings. A public Facebook group devoted to sharing destructive experiences with the G7 has grown to hundreds of customers, and several other class action lawsuits have been filed towards the corporate, alleging false advertising and misleading claims about machine accuracy.
But, primarily based on a normal metric within the trade, the G7 is without doubt one of the most correct glucose sensors out there. “Accuracy within the efficiency of our machine is our primary precedence. We perceive this can be a lifesaving machine for folks with Sort 1 diabetes,” Peter Simpson, Dexcom’s senior vp of innovation and sensor know-how, instructed IEEE Spectrum. Simpson acknowledged some variability in particular person sensors, however stood by the accuracy of the units.
So why have customers confronted points? Partly, metrics utilized in advertising and marketing might be deceptive in comparison with actual world efficiency. Variations in research design, mixed with advanced organic realities, imply that the accuracy of those biosensors can’t be boiled down to 1 quantity—and customers are studying this the arduous means.
Dexcom’s Glucose Displays
Steady glucose displays (CGMs) usually include a small filament inserted beneath the pores and skin, a transmitter, and a receiver. The filament is coated with an enzyme that generates {an electrical} sign when it reacts with glucose within the fluid surrounding the physique’s cells. That sign is then transformed to a digital sign and processed to generate glucose readings each couple of minutes. Every sensor lasts every week or two earlier than needing to get replaced.
The know-how has come a good distance lately. Within the 2010s, these units required blood glucose calibrations twice a day and nonetheless weren’t dependable sufficient to dose insulin primarily based on the readings. Now, some insulin pumps use the near-real-time knowledge to automatically make adjustments. With these enhancements has come larger belief within the knowledge customers obtain—and better requirements. A defective studying might lead to a harmful dose of insulin.
The G7 launched a number of modifications to Dexcom’s earlier designs, together with a a lot smaller footprint, and up to date the algorithm used to translate sensor alerts into glucose readings for higher accuracy, Simpson says. “From a efficiency perspective, we did show in a scientific trial that the G7 is considerably extra correct than the G6,” he says.
So Heller and others had been shocked when the brand new Dexcom sensor appeared to be performing worse. For some batches of sensors, it’s doable that the difficulty was partially on account of an unvalidated change in a element utilized in a resistive layer of the sensors. The brand new element confirmed worse efficiency, in keeping with a warning letter issued by the U.S. Meals and Drug Administration in March 2025, following an audit of two U.S. manufacturing websites. The fabric has since been faraway from all G7 sensors, Simpson says, and the corporate is continuous to work with the FDA to handle issues. (“The warning letter doesn’t prohibit Dexcom’s capability to supply, market, manufacture or distribute merchandise, require recall of any merchandise, nor prohibit our capability to hunt clearance of recent merchandise,” Dexcom added in a press release.)
“There’s a distribution of accuracies that must do with folks’s physiology and in addition the units themselves. Even in our scientific research, we noticed some that had been actually exact and a few that had a bit of little bit of inaccuracy to them,” says Simpson. “However typically, our sensor may be very correct.”
In late November Abbott—considered one of Dexcom’s important rivals—recalled some of its CGMs on account of inaccurate low glucose readings. The recall impacts roughly 3 million sensors and was brought on by a difficulty with considered one of Abbott’s manufacturing strains.
The discrepancy between reported accuracy and user experience, nonetheless, goes past anyone firm’s manufacturing missteps.
Does MARD Matter?
The accuracy of CGM programs is regularly measured through “imply absolute relative distinction,” or MARD, a proportion that compares the sensor readings to laboratory blood glucose measurements. The decrease the MARD, the extra correct the sensor.
This quantity is commonly utilized in promoting and advertising and marketing, and it has a historic relevance, says Manuel Eichenlaub, a biomedical engineer on the Institute for Diabetes Technology Ulm in Germany, the place he and his colleagues conduct impartial CGM efficiency research. For years, there was a general belief {that a} MARD beneath 10 p.c meant a system could be correct sufficient for use for insulin dosing. In 2018, the FDA established a selected set of accuracy requirements past MARD for insulin-guiding glucose displays, together with Dexcom’s. However producers design the scientific trials that decide accuracy metrics, and the way in which research are designed could make an enormous distinction.
When Dan Heller wore the Dexcom G6 and G7 on the similar time, he says he observed the G7 readings had been extra erratic, making it tougher to correctly management his blood sugar. Dan Heller
As an illustration, blood glucose ranges function the “floor fact to check the CGM values towards,” says Eichenlaub. However glucose ranges fluctuate throughout blood compartments within the physique; blood collected from capillaries with a finger prick fluctuates extra and may have glucose ranges round 5 to 10 p.c greater than venous blood. (Dexcom exams towards a gold-standard venous blood analyzer. When customers see inaccuracies towards residence meters that use capillary blood, it might partially be a mirrored image of the meter’s personal inaccuracy, Simpson says, although he acknowledges actual inaccuracies in CGMs as nicely.)
Moreover, the distribution of sampling isn’t standardized. CGMs are recognized to be much less correct at the start and finish of use, or when glucose ranges are out of vary or altering shortly. Which means measured accuracy could possibly be skewed by taking fewer samples proper after a meal or late within the CGM’s lifetime.
In accordance with Simpson, Dexcom’s trial protocol meets the FDA’s expectation and exams the units in numerous blood sugar ranges throughout the lifetime of the sensor. “Inside these scientific trials, we do stress the sensors to attempt to simulate these actual world circumstances,” he says.
Dexcom and different firms promote a MARD round 8 p.c. However some impartial research are extra demanding and discover greater numbers; a head-to-head study of three popular CGMs that Eichenlaub led discovered MARD values nearer to 10 p.c or greater.
Eichenlaub and different CGM consultants consider that extra standardization of testing and an extension of the FDA necessities are crucial, so that they recently proposed comprehensive guidelines on CGM efficiency testing. In america and Europe, just a few producers at present dominate the market. However newer gamers are getting into the rising market and, particularly in Europe, could not meet the identical requirements as legacy producers, he says. “Having a standardized means of evaluating the efficiency of these programs is essential.”
For customers like Heller although, higher accuracy solely issues if it yields higher diabetes administration. “I don’t care about MARD. I would like knowledge that’s reliably actionable,” Heller says. He encourages engineers engaged on these units to assume just like the affected person. “Sooner or later, there’s quantitative knowledge, however you want qualitative knowledge.”
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