Several CGM systems are currently available on the market, each with its unique features and specifications:
Components: These systems typically consist of a sensor (subcutaneous needle) with its applicator, a transmitter (in most systems directly attached to the sensor), and the receiver or ‘reader’ (which can be a smartphone or a separate device).
Calibration Requirements: Some systems require frequent calibration twice a day with fingerstick tests, while others are factory-calibrated and do not require fingerstick calibration.
Wear Time: Depending on the system, this can range from a few days to several weeks.
Importantly, CGM provides a more comprehensive and real-time view of glycaemic management daily, offering insights that HbA1c cannot capture [67, 72]. As a result, CGM-derived metrics have become increasingly important, with new metrics being developed to reflect different aspects of glycaemic management [36, 69, 73, 76]. Time in range (TIR), time in hypo- and hyperglycaemia, and glycaemic variability (GV) are now recognised as integral components of glucose management [36, 73, 77], and these parameters have been shown to improve after starting CGM [78].
Interpreting CGM Data
Time in Range (TIR)
TIR is the percentage of time a person spends within their target glucose range (usually 70-180 mg/dL or 3.9-10.0 mmol/L) over a given period. The aim is to maximise TIR and minimise the time spent in hypoglycaemia (<70 mg/dL or <3.9 mmol/L) and hyperglycaemia (>180 mg/dL or >10.0 mmol/L) [36, 73, 79].
In 2019, an international consensus statement provided recommendations for the time spent in these specific glucose ranges [79]. For adults with T1D, a target range of 70-180 mg/dL (3.9-10.0 mmol/L) and recommended TIR of >70% were established (Figure 7), but an individualised approach is advised [77, 79, 80]. The latest ADA Standards of Medical Care in Diabetes 2024 specifically highlight the importance of TIR for the assessment of glycaemic management, in addition to HbA1c [74], also since TIR was found to be associated with the development of diabetic complications [81-84].