The present study has a prospective, observational design and aimed to test the accuracy of the Dexcom G6 rt-CGM during moderate exercise. Measurements were performed in 2 consecutive time periods; first 6 days with moderate exercise, followed by 6 days with only normal daily activities (NDA). This study was approved by the Medical Ethical committees in The Netherlands (Isala Hospital; NL70456.075.19/190605) and in Spain (CEIm de las Áreas de Salud de León y del Bierzo; no.1981). Registered at www.trialregister.nl: NL7922. All participants gave written informed consent prior to the start of the study. All study procedures were performed in accordance with relevant guidelines and regulations.
Measurements were performed during the Bas van de Goor Foundation (a non-profit organization aiming to stimulate exercise among persons with diabetes) ‘wehike2changediabetes’ challenge in September 2019. During this challenge, persons with T1DM from Spain and The Netherlands hiked from Astorga to Santiago de Compostela, over a total distance of 110.19 km and a variable amount of altitude meters spread over the days (in total 2334 meters). The inclusion criteria to participate were adult age (> 18 years), having T1DM and the ability to provide oral and written informed consent. All participants (n=17) of the challenge agreed to participate in the present study and provided (written) informed consent.
Dexcom G6 rt-CGM devices were implanted in the back of the upper arm; all device related procedures were performed according to operating instructions. Capillary self-measurements of blood glucose (SMBG) reference measurements were performed with Precision Neo Pro strips (Free Style Libre Capillary glucose measurement strip = FSLCstrip) . This capillary measurement strip was previously verified to be comparable with NIST standards to the gold reference method isotope dilution mass spectrometry [7, 8]. Participants were asked to perform a total of (at least) 7 capillary SMBG per day. Participants were also instructed to perform extra SMBG if necessary, for instance when experiencing symptoms related to hypoglycemia. The SMBG results were not used to calibrate the Dexcom G6 rt-CGM.
Data from both the Dexcom G6 rt-CGM and capillary SMBG readings were extracted at the end of the study. The online software program Dexcom Clarity was used to gather the information of all glucose measurements, produced every 5 minutes by the Dexcom G6 rt-CGM of the participants. The readings of the Dexcom G6 rt-CGM that are closest in time (with a maximum window of two minutes) of the FSLC readings were used for calculations.
Primary outcome of this study was the accuracy of the Dexcom G6 rt-CGM during the 6-day exercise period. As secondary outcomes the accuracy of the Dexcom G6 rt-CGM was analyzed during the 6-day period with NDA. In addition, comparisons between the Dexcom G6 rt-CGM and the capillary reference glucose during moderate exercise and NDA were made.
Accuracy of the Dexcom G6 rt-CGM was analyzed according to the Integrated Continuous Glucose Monitoring Approvals (Class II–510(K) guidelines (ICGMA) guidelines  and results of both testing periods were compared using a paired t-test. Comparisons between exercise and NDA were analyzed using Parkes error grid analysis . The accuracy of Dexcom G6 rt-CGM derived glucose values versus capillary reference glucose values was determined as % within the error grid zones. Values in zones A and B are deemed clinically acceptable, whereas those in zones C, D and E are considered potentially unsafe. Correlation analysis, a parameter using the intraclass correlation coefficient (ICC) was performed to assess the correlation between the sensor value and reference values . For bias analysis, mean absolute differences (MAD), and mean absolute relative differences (MARD) were calculated. A significance level of 5% was considered significant. Analyses were performed using SPSS (IBM SPSS Statistics, version 25.0. Armonk, NY: IBM Corp.) and Microsoft Excel Analyse-It (2010).