This cross-sectional study was conducted at Centro Hospitalar Universitário de São João (CHUSJ), Porto, Portugal. We included patients with T1D followed in the outpatient clinic between 2020 and 2022 using the intermittent scanned CGM system Freestyle Libre (is-CGM). This study was approved by the Ethical Committee of CHUSJ.

Clinical data was collected from electronic health records and is-CGM data was collected from the cloud-based system LibreView.

We included patients aged 18 years or older with T1D using the CGM system Freestyle Libre. Participants were identified from the list of patients associated with CHUSJ in the LibreView platform. We excluded repeated accounts, patients with other types of diabetes, patients without is-CGM data uploads, patients without HbA1c evaluations, and patients without active sensor time of at least 70% at the time of HbA1c evaluation (Supplementary Fig. 1).

The following parameters were obtained from the electronic health records: gender, age, and education (less than high school graduate; high school graduate; some college education; college degree or higher), duration of diabetes, hypertension (defined as previously diagnosed hypertension or treatment with blood pressure lowering drugs), systolic and diastolic blood pressure, dyslipidemia (defined as a previous diagnosis, under lipid-lowering drugs); type of diabetes treatment (insulin pens or insulin pumps); use of other antidiabetic drugs; anthropometric parameters (weight, height, and body mass index). HbA1c levels and lipid profiles (total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides) were obtained from routine laboratory evaluations.

The following parameters were obtained from the LibreView platform (data from 14 days): time CGM is active, TIR (70–180 mg/dL), time below range (TBR, < 70 mg/dL), time below 54 mg/dL (TB54), time above range (TAR, > 180 mg/dL), time above 250 mg/dL (TA250), coefficient of variation (CV) and glucose management indicator (GMI).

Complications of diabetes were obtained from electronic health records. Any complication was defined as having microvascular or macrovascular complication.

The following microvascular complications were collected: retinopathy (defined as any degree of retinopathy in ophthalmologic evaluation), nephropathy (defined as a confirmed value of albumin to creatinine ratio of 30 mg/g or greater, or eGFR of less than 60 mL/min/1.73 m2), diabetic peripheral neuropathy (defined by a change in the assessment of 10-g monofilament testing or changes in temperature or pinprick sensation). The following macrovascular complications were collected: ischemic coronary disease (defined as a history of myocardial infarction, stable or unstable angina, or myocardial revascularization), cerebrovascular disease (characterized as a history of stroke or transient ischemic attack) and peripheral arterial disease (defined as a history of intermittent claudication, ankle-brachial index ≤ 0.90 or lower-extremity revascularization). Heart failure diagnosis was also assessed (defined by clinical diagnosis of heart failure or previous hospitalization due to the same pathology).

Continuous variables are described as mean ± standard deviation and categorical variables as proportions (percentages).

The associations of CGM-metrics and HbA1c with any complication, microvascular complications, and macrovascular complications were assessed by logistic regression unadjusted and adjusted for age, sex, and duration of diabetes (model 1), and further adjusted for hypertension and dyslipidemia (model 2). For the individual components of macrovascular complications and diabetic peripheral neuropathy, only the unadjusted analysis was performed due to the low number of events.

All analyses were conducted with the statistical software package Stata IC version 17.0 (College Station, TX). A two-sided P-value < 0.05 was considered statistically significant.