Hypoglycaemia is less common with CGM than SMBG despite achieving the same HbA1c

International Time in Range consensus guidelines recommend that continuous glucose monitoring (CGM) users aim to spend less than 4% of time with blood glucose levels under 3.9 mmol/L and less than 1% with levels under 3.0 mmol/L. However, these recommendations are largely based on studies of sensor-augmented insulin pump therapy, whereas most people with type 1 diabetes, including CGM users, use multiple daily insulin injections (MDI).

This study sought to compare time in hypoglycaemia and HbA_1c levels between users of CGM and self-monitoring of blood glucose (SMBG) who were on MDI therapy. A total of 161 people were randomised to either CGM or SMBG for 6 months, followed by the other therapy for a further 6 months, with a 17-week washout period in between. Masked CGM was used in two of the last four weeks of the SMBG treatment phase to compare glucose metrics. Follow-up data were available for 137 participants.

Overall, the lower the HbA_1c achieved, the more time was spent in hypoglycaemia in both CGM and SMBG users. Generally, these participants on MDI therapy found it harder to achieve both HbA_1c and hypoglycaemia targets than insulin pump users in previous studies.

At all HbA_1c levels, CGM users spent less time in hypoglycaemia than SMBG users. For instance, to achieve an HbA_1c of <53 mmol/mol (7.0%), CGM users spent 5.4% of time with glucose levels under 3.9 mmol/L, compared with 9.2% of the time for SMBG users, and the two groups spent 1.5% versus 3.5% of time in grade 2 hypoglycaemia (<3.0 mmol/L). Similar patterns were observed when using Time In Range and mean blood glucose levels as the measure of glycaemic control.

The authors conclude that achieving both HbA_1c and Time Below Range targets is challenging for people with type 1 diabetes treated with MDI, both with CGM and SMBG. However, CGM is associated with considerably less time in hypoglycaemia than SMBG at a broad range of HbA_1c levels. They argue that CGM is crucial for individuals on MDI treatment if they are to achieve HbA_1c targets and simultaneously avoid hypoglycaemia.

Seyed Ahmadi S, Westman K, Pivodic A et al (2020) The association between HbA_1c and time in hypoglycemia during CGM and self-monitoring of blood glucose in people with type 1 diabetes and multiple daily insulin injections: a randomized clinical trial (GOLD-4). Diabetes Care 8 Jul [epub ahead of print]. https://doi.org/10.2337/dc19-2606

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