In the summer of 2024, we conducted a CGM study out of our own interest and largely self-financed. In the study, the performance of the current Dexcom G7 and FreeStyle Libre 3 systems and the new system from Medtronic called Simplera were tested in parallel. The main research question was how well the individual systems matched different comparison methods. We also wanted to analyze how well recently proposed study procedures could be implemented in practice. The remarkable about this procedure is that the CGM systems are tested under essential clinically relevant conditions, including rapidly changing glucose levels, and thus reflect the real lives of people with type 1 diabetes. However, particularly these conditions often challenge the accuracy of CGM systems. Furthermore, the study allowed us to compare various parameters that provide information about glycemic control, such as the time in the target range between 70 and 180 mg/dl, between the CGM systems.
24 adults with type 1 diabetes participated in the study and wore a sensor from each of the three systems in parallel for 15 days (Figure 1). Due to the different sensor lifetimes (Libre 3: 14 days, Dexcom G7: 10 days and Medtronic Simplera 7 days), the sensors from Dexcom and Medtronic had to be changed once during the study. To record comparison measurements, the participants were invited to our institute on three days (days 2, 5 and 15) for a session of several hours. Here, blood glucose measurements were taken every 15 minutes over seven hours using capillary and venous blood on different measuring devices. During this time, the study participants underwent a so-called glucose excursion. To do this, they were asked to eat a breakfast with a high proportion of carbohydrates and to delay the corresponding meal insulin delivery. This causes the blood glucose to rise quickly above 300 mg/dl, then drop again relatively quickly and even triggers a brief hypoglycemia (Figure 2). This allows us to test the CGM systems at high and low glucose values and at rapid rates of change. The participants spent the remaining study days at home and went about their daily lives.
We were able to show that the newly proposed test procedure is feasible in principle and safe for the study participants. All clinically relevant conditions could be reproduced sufficiently well at the study center to achieve the desired distribution of blood glucose values.
The CGM systems Libre 3 and Dexcom G7 showed a similar performance, while Medtronic Simplera deviated more from the comparison methods. It systematically displayed lower values, which meant, for example, that the rapid increases in blood glucose were not recorded accordingly. In general, however, the resulting measurement accuracy of the systems depended on which measurement method they were compared with (Figure 3). This illustrates once again that there is an urgent need to standardize the test procedures for CGM systems as far as possible to be able to assess the quality of individual systems better. Our institute has been pursuing this goal for several years as part of its activities in the CGM working group of the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), which was led by Dr. Freckmann from 2019 to 2024 and by Dr. Pleus from the IfDT since 2025.
When comparing the therapy parameters, there were also differences between Libre 3 and Dexcom G7 on the one hand and Medtronic Simplera on the other (Figure 4). In particular, the time in the target range of 70 to 180 mg/dl should be emphasized here, where differences of approx. 8% were seen on average. This means that the Medtronic Simplera displayed approx. two hours longer in the target range per day, and therefore, the quality of glucose control appeared significantly better. A uniform comparative measurement procedure for all manufacturers could bring significant improvements here, which is another vital reason for standardization.
Many thanks to everyone who participated in this study!
Detailed information on our study can be found in the full-text publications in international journals.
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