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 era on the identical 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 1000’s of individuals with Kind 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 submit on his Substack, which is devoted to protecting Kind 1 diabetes analysis and administration, he wrote about the experience and predicted a rise in antagonistic occasions with the G7, drawing on his previous expertise main tech and biotech corporations.
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 studies of erratic, inaccurate readings. A public Facebook group devoted to sharing detrimental experiences with the G7 has grown to 1000’s of customers, and several other class action lawsuits have been filed towards the corporate, alleging false advertising and misleading claims about machine accuracy.
But, based mostly on a typical metric within the business, the G7 is likely one of the most correct glucose sensors out there. “Accuracy within the efficiency of our machine is our primary precedence. We perceive it is a lifesaving machine for folks with Kind 1 diabetes,” Peter Simpson, Dexcom’s senior vice chairman of innovation and sensor expertise, advised IEEE Spectrum. Simpson acknowledged some variability in particular person sensors, however stood by the accuracy of the gadgets.
So why have customers confronted points? Partially, metrics utilized in advertising and marketing may be deceptive in comparison with actual world efficiency. Variations in examine 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 exhausting method.
Dexcom’s Glucose Screens
Steady glucose displays (CGMs) sometimes include a small filament inserted below 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 expertise has come a good distance lately. Within the 2010s, these gadgets required blood glucose calibrations twice a day and nonetheless weren’t dependable sufficient to dose insulin based mostly 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 end in 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 exhibit 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 attainable that the problem was partly resulting from an unvalidated change in a element utilized in a resistive layer of the sensors. The brand new element confirmed worse efficiency, in line 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 deal with issues. (“The warning letter doesn’t prohibit Dexcom’s potential to provide, market, manufacture or distribute merchandise, require recall of any merchandise, nor prohibit our potential to hunt clearance of recent merchandise,” Dexcom added in a press release.)
“There’s a distribution of accuracies that need to do with folks’s physiology and in addition the gadgets themselves. Even in our scientific research, we noticed some that had been actually exact and a few that had just a little little bit of inaccuracy to them,” says Simpson. “However usually, our sensor may be very correct.”
In late November Abbott—certainly one of Dexcom’s most important opponents—recalled some of its CGMs resulting from inaccurate low glucose readings. The recall impacts roughly 3 million sensors and was brought on by a problem with certainly one of Abbott’s manufacturing strains.
The discrepancy between reported accuracy and user experience, nevertheless, goes past anyone firm’s manufacturing missteps.
Does MARD Matter?
The accuracy of CGM programs is incessantly measured by way of “imply absolute relative distinction,” or MARD, a share 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 unbiased CGM efficiency research. For years, there was a general belief {that a} MARD below 10 p.c meant a system could be correct sufficient for use for insulin dosing. In 2018, the FDA established a particular 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 best way research are designed could make a giant distinction.
When Dan Heller wore the Dexcom G6 and G7 on the identical time, he says he observed the G7 readings had been extra erratic, making it harder to correctly management his blood sugar. Dan Heller
As an example, blood glucose ranges function the “floor reality to match the CGM values towards,” says Eichenlaub. However glucose ranges range throughout blood compartments within the physique; blood collected from capillaries with a finger prick fluctuates extra and might have glucose ranges round 5 to 10 p.c increased than venous blood. (Dexcom checks towards a gold-standard venous blood analyzer. When customers see inaccuracies towards residence meters that use capillary blood, it might partly be a mirrored image of the meter’s personal inaccuracy, Simpson says, although he acknowledges actual inaccuracies in CGMs as effectively.)
Moreover, the distribution of sampling isn’t standardized. CGMs are identified to be much less correct at first and finish of use, or when glucose ranges are out of vary or altering rapidly. Which means measured accuracy might 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 checks the gadgets in several blood sugar ranges throughout the lifetime of the sensor. “Inside these scientific trials, we do stress the sensors to try to simulate these actual world situations,” he says.
Dexcom and different corporations promote a MARD round 8 p.c. However some unbiased research are extra demanding and discover increased numbers; a head-to-head study of three popular CGMs that Eichenlaub led discovered MARD values nearer to 10 p.c or increased.
Eichenlaub and different CGM consultants consider that extra standardization of testing and an extension of the FDA necessities are needed, in order that they recently proposed comprehensive guidelines on CGM efficiency testing. In america and Europe, a couple of producers at the moment dominate the market. However newer gamers are coming into the rising market and, particularly in Europe, could not meet the identical requirements as legacy producers, he says. “Having a standardized method 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 gadgets to suppose just like the affected person. “Sooner or later, there’s quantitative knowledge, however you want qualitative knowledge.”
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