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 transport 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 masking Kind 1 diabetes analysis and administration, he wrote about the experience and predicted a rise in opposed 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 gadget. Some complaints regard failed connection and deployment points, which Dexcom claims to have now addressed. Extra regarding are experiences of erratic, inaccurate readings. A public Facebook group devoted to sharing unfavorable 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 gadget accuracy.
But, primarily based on a normal metric within the trade, the G7 is likely one of the most correct glucose sensors out there. “Accuracy within the efficiency of our gadget is our primary precedence. We perceive it is a lifesaving gadget for individuals with Kind 1 diabetes,” Peter Simpson, Dexcom’s senior vice chairman of innovation and sensor know-how, informed 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 might 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 at least one quantity—and customers are studying this the arduous manner.
Dexcom’s Glucose Displays
Steady glucose screens (CGMs) sometimes include a small filament inserted underneath 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 jiffy. Every sensor lasts per week or two earlier than needing to get replaced.
The know-how has come a great distance lately. Within the 2010s, these gadgets 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 information to automatically make adjustments. With these enhancements has come higher belief within the information 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 exhibit in a scientific trial that the G7 is considerably extra correct than the G6,” he says.
So Heller and others have 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 attributable to an unvalidated change in a element utilized in a resistive layer of the sensors. The brand new element confirmed worse efficiency, in response to 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 constant to work with the FDA to handle considerations. (“The warning letter doesn’t prohibit Dexcom’s means to provide, market, manufacture or distribute merchandise, require recall of any merchandise, nor prohibit our means to hunt clearance of latest merchandise,” Dexcom added in an announcement.)
“There’s a distribution of accuracies that should do with individuals’s physiology and in addition the gadgets themselves. Even in our scientific research, we noticed some that have been actually exact and a few that had slightly little bit of inaccuracy to them,” says Simpson. “However typically, our sensor may be very correct.”
In late November Abbott—one in all Dexcom’s most important opponents—recalled some of its CGMs attributable to inaccurate low glucose readings. The recall impacts roughly 3 million sensors and was brought on by a problem with one in all Abbott’s manufacturing traces.
The discrepancy between reported accuracy and user experience, nonetheless, goes past anybody firm’s manufacturing missteps.
Does MARD Matter?
The accuracy of CGM techniques is ceaselessly 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 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 underneath 10 % meant a system can 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 screens, 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 have 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 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 % greater than venous blood. (Dexcom checks towards a gold-standard venous blood analyzer. When customers see inaccuracies towards dwelling 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 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.
Based on 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 attempt to simulate these actual world situations,” he says.
Dexcom and different firms promote a MARD round 8 %. 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 % or greater.
Eichenlaub and different CGM specialists 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 the US and Europe, a couple of producers at the moment 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 manner of evaluating the efficiency of these techniques 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 information that’s reliably actionable,” Heller says. He encourages engineers engaged on these gadgets to assume just like the affected person. “In some unspecified time in the future, there’s quantitative information, however you want qualitative information.”
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