It's nice when my predictions prove correct. One example: following the ADA 84th Scientific Sessions in 2024, I made a prediction (see https://blog.sstrumello.com/2024/07/abbotts-freestyle-libre-3-plus-may-push.html for more on my prediction) that Abbott's move to increase wear-time on its sensors would force Dexcom to respond with a longer-wearing CGM sensor of its own, and that's now happened.
I surmised that based on the fact that Abbott (which makes the Freestyle Libre CGM system) introduced a longer-wearing FreeStyle Libre 3 Plus which lasts for 15 days (as opposed to only 14 days on Libre 3 sensor), substantiated by hints from Dexcom CEO Kevin Sayer that Dexcom was working towards a longer-wearing G7 sensor, although he cited issues with the adhesive lasting long enough to ensure its 15-day G7 Plus sensor lasts its entire useful life as the reason for not doing so when the G7 launched. However, remember that Dexcom's G7 and Stelo use the exact same CGM sensor, only the wear-time for Stelo was already 15 days versus a mere 10 days for the regular Dexcom G7, hence I was calling Kevin Sayer out for a misleading statement. It had more to do with milking as much cash out of the shorter 10-day G7 sensors for the financial benefit of Dexcom shareholders. But the competition from Abbott eventually forced Dexcom to respond with a longer-wearing sensor of its own.
Last week [on April 10, 2025], Dexcom announced it received FDA approval (see the press release at https://www.businesswire.com/news/home/20250410304660/en/Dexcom-G7-15-Day-Receives-FDA-Clearance-the-Longest-Lasting-Wearable-and-Most-Accurate-CGM-System) for a new, longer-lasting Dexcom G7 15 Day sensor. The consensus among patients I have spoken with is that longer wear-time was the least Dexcom could do for patients given how erroneous the first day of each Dexcom G7 sensors actually are. Many are still concerned about the longevity of the sensor adhesive (Skin-Tac adhesive, anyone?) and the fact that Dexcom weighs more than Libre so the sensors are less likely to last for the full 15 days than Abbott Libre 3 Plus sensors are to last.
To be sure, the Dexcom G7 15 Day sensor is still no longer than Abbott's Freestyle Libre 3 Plus sensor. But it is an improvement of the longevity on Dexcom's regular G7 CGM sensor which has a miserly 10-day wear-time. As for the accuracy claims made in Dexcom's G7 Plus press release, those are bogus, or at best, misleading.
MARD is a widely used metric for CGM accuracy, but its lack of standardization has led to significant concerns. The primary critique revolves around the fact that different CGM manufacturers calculate MARD using varying [different] methodologies, making direct comparisons of accuracy between CGM devices unreliable at best.
Some key issues include:
- Variability in Reference Measurements: Manufacturers may use different reference glucose measurements (e.g., venous plasma, capillary blood, or laboratory-calibrated values), which can affect the reported MARD.
- Differences in Time Matching: The timing of CGM readings compared to reference values can vary, leading to inconsistencies in accuracy assessments.
- Data Selection Bias: Some manufacturers may exclude outlier data or use specific subsets of readings to improve their reported MARD, making it appear more favorable than it would be in real-world conditions.
- Lack of Regulatory Standardization: Since the FDA does not enforce a universal calculation method, manufacturers have flexibility in how they report MARD, leading to discrepancies in accuracy claims.
For more background on the critical assessments of Mean Absolute Relative Difference (MARD) as it is currently used by the U.S. Food and Drug Administration, please refer to:
- https://diabetesjournals.org/care/article/46/10/1825/153465/Real-world-Accuracy-of-CGM-in-Inpatient-Critical
- https://diabetesjournals.org/spectrum/article/35/4/405/147875/The-Devil-Is-in-the-Details-Use-Limitations-as
- https://diabetesjournals.org/care/article/48/2/259/157542/Continuous-Glucose-Monitor-Accuracy-for-Diabetes
The critique has led to some calls for more standardized accuracy metrics, such as the Clarke Error Grid or Consensus Error Grid, which might provide a more clinically relevant assessment of CGM performance over MARD.
Anyway, on price, Dexcom's 15-day G7 sensor means patient out-of-pocket costs will be coming down. Given erroneous first day readings many patients experience on the G7, in reality, the longer-wearing sensor gives patients more like 14 days of sensor usage rather than 15 days.
Still, it's nice when my predictions are proven correct, as mine was when Abbott introduced a longer-wearing CGM sensor, which forced competitor Dexcom to match it. Patients may still prefer Abbott's Libre 3 Plus over Dexcom's G7 Plus. Not only is Abbott Freestyle Libre 3 Plus smaller in size than Dexcom G7 Plus, but Libre 3 Plus provides 1440 new readings each day compared to a mere 288 new readings with Dexcom G7 Plus. The one downside with Libre is no calibrations although Dexcom pretty much ignores the calibrations anyway. Better to have more readings IMHO. With manufacturer coupons (which I covered at https://blog.sstrumello.com/2023/12/abbott-gets-real-about-formulary.html for more information) means that it really does come down to patient preference for which CGM better meets their needs.
Increasingly, many patients are choosing Abbott rather than Dexcom to due Abbott Libre's unique product advantages. That, combined with third-party apps enabling Libre 3 Plus readings such as Sweet Dreams – Sugar Tracker on Apple Watch (see my coverage at https://blog.sstrumello.com/2024/05/get-abbott-freestyle-libre-3-readings.html for more about that) means that Dexcom's longstanding market dominance does not look so well-protected anymore.