Research in context
Evidence before this study
We searched PubMed for trial reports published in English up to Feb 2, 2021, comparing real-time continuous glucose monitoring (rtCGM) with intermittently scanned continuous glucose monitoring (isCGM) in non-pregnant adults with type 1 diabetes. We used search terms “intermittent” or “flash”, “real time”, “continuous glucose monitoring”, and “type 1 diabetes”. We identified six manuscripts of four trials. Three manuscripts were based on the randomised controlled I HART trial, one was the randomised controlled CORRIDA trial, and two described observational trials, evaluating real-world data from France, Germany, and Austria.
The I HART trial by Reddy and colleagues was an 8-week trial, followed by an 8-week extension phase, done in 40 adults with type 1 diabetes and impaired awareness of hypoglycaemia, treated with multiple daily insulin injections. Median glycated haemoglobin (HbA1c) was 7·3% (56 mmol/mol). The CORRIDA trial by Hásková and colleagues studied 60 adults with type 1 diabetes and normal hypoglycaemia awareness during a 4-day exercise and 4-week home phase. Mean HbA1c was 7·8% (62 mmol/mol). Both trials included CGM naive people. Of note, outcomes regarding glycaemic control were not measured with the same CGM device in the I HART trial, which is an important limitation of the study design.
The French observational trial by Préau and colleagues assessed the effect of switching from isCGM to rtCGM in 18 adults with type 1 diabetes and a high risk of hypoglycaemia (n=8), or an elevated HbA1c (n=9), or both (n=2) after 3 and 6 months. Mean HbA1c was 8·07% (65 mmol/mol). The German and Austrian trial by Sandig and colleagues included 233 adults with type 1 diabetes using isCGM or rtCGM, with a median HbA1c of 7·3% (56 mmol/mol), in a cross-sectional analysis. In both observational studies, most participants used insulin pump therapy.
I HART, CORRIDA, and the observational trials concluded that rtCGM was superior to isCGM with regard to glycaemic control based on CGM metrics; time in range (sensor-glucose 3·9–10·0 mmol/L [70 to 180 mg/dL]) was higher, while time in hypoglycaemia (definitions ranged from sensor-glucose <3·0 mmol/L [54 mg/dL] to <3·9 mmol/L [70 mg/dL]) was lower with rtCGM than with isCGM. Additionally, the I HART trial showed less worry about hypoglycaemia with the use of rtCGM. Only two trials evaluated HbA1c and observed no benefit with rtCGM versus isCGM. However, as trials were limited in terms of study population (small and prespecified), design, and duration (short follow-up), it is still not clear whether switching from isCGM to rtCGM with alert functionality offers additional benefits in a large and unselected population with type 1 diabetes over a longer period of time.
Added value of this study
The ALERTT1 trial is the first 6-month, multicentre, prospective, randomised controlled trial comparing rtCGM with isCGM in 254 adults with type 1 diabetes, who previously used isCGM. Mean HbA1c was 7·4% (58 mmol/mol) and a minority of the study population was hypoglycaemia unaware (44 [17%] people) or had a history of severe hypoglycaemia (29 [11%]). Most (205 [81%]) were treated with multiple daily injections. Findings showed that in an unselected group of people with type 1 diabetes, 6-month use of rtCGM with alert functionality improved time in range (sensor-glucose 3·9–10·0 mmol/L [70–180 mg/dL]), while HbA1c, time in clinically significant hypoglycaemia (sensor-glucose <3·0 mmol/L [54 mg/dL]), and time in hyperglycaemia (sensor-glucose >10·0 mmol/L [180 mg/dL]) were reduced. Aditionally, more people on rtCGM achieved glycaemic targets as defined by international consensus guidelines, and had less frequently severe hypoglycaemia.
Besides glycaemic control, the ALERTT1 trial also evaluated patient reported outcomes through various validated questionnaires. Despite relatively high quality of life of all participants at baseline, rtCGM users experienced less hypoglycaemia worry and higher treatment satisfaction at the end of study.
Implications of all the available evidence
People using rtCGM showed significant benefits over 6 months compared with people using isCGM in terms of both glycaemic control and patient reported outcomes. This implies that clinicians should consider rtCGM to improve the health and quality of life of people living with type 1 diabetes.