The present study wants to compare the Dexcom G6® continuous glucose monitoring (CGM) system (experimental group) with the FreeStyle Libre flash glucose monitoring (FGM) system (control group).

The ALERTT1 trial will have three phases: a baseline, study, and extension phase.

During the baseline phase, eligible patients will be screened for in- and exclusion criteria, wear a blinded Dexcom G6® for 28 days, together with their FreeStyle Libre FGM system, and receive a uniform education moment.

In the study phase, patients will be randomized into two groups (1:1): the experimental group will use an unblinded Dexcom G6® CGM for 6 months, the control group will keep using the FreeStyle Libre FGM system for 6 months. Before the 6 month time point is reached, patients in the control group will wear a blinded Dexcom G6® CGM for 28 days, together with their FreeStyle Libre FGM.

In the extension phase, patients in the initial control group will start using unblinded Dexcom G6® for 30 months. The initial experimental group will keep using the unblinded Dexcom G6® for the next 30 months.

Inclusion Criteria:

• signed ICF
• diagnosis of type 1 diabetes ≥6 months
• using FreeStyle Libre FGM system ≥6 months
• intensified insulin therapy/insulin pump therapy
• HbA1c ≤10%
• willing to wear the glucose monitoring device >80% of the time
• willing to download glucose monitoring data at regular intervals

Exclusion Criteria:

• non-type 1 diabetes participants or diagnosis <6 months
• participant with T1D not on insulin, or on non-intensified insulin therapy
• pregnancy or planning pregnancy within next 6 months
• severe cognitive dysfunction or other disease which makes sensor use difficult
• current treatment with drugs known to have significant interference with glucose metabolism, such as systemic corticosteroids, as judged by the investigator
• abnormal skin at the anticipated glucose sensor insertion sites (excessive hair, burn, inflammation, infection, rash, and/or tattoo)
• presence of concomitant pathology that might cause edema at the insertion sites (such as heart failure, liver failure, kidney failure defined as eGFR <30 mL/min [stage ≥4])
• beta-cell transplantation and c-peptide positive and/or under immunosuppressive therapy

Anonymous data can be shared with participating centers, based on research questions mentioned in this protocol or based on a new study protocol approved by the relevant ethical committees.