Associations between HbA_1c and continuous glucose monitoring-derived glycaemic variables

To identify clinically useful associations between HbA_1c levels and various continuous glucose monitoring-derived metrics.

We retrospectively analysed end-of-study HbA_1c levels and >2 weeks of continuous glucose monitoring data collected from 530 adults with Type 1 diabetes or insulin-requiring Type 2 diabetes during four randomized trials. Each trial lasted ≥24 weeks and provided central laboratory end-of-study HbA_1c levels and continuous glucose monitoring data from the preceding 3 months. Participants were assigned to groups based on either HbA_1c levels or continuous glucose monitoring-derived glucose values.

HbA_1c was strongly correlated with mean glucose value (r=0.80), time spent with glucose values in the 3.9-10.0 mmol/l range (time in range; r=-0.75) and percentage of glucose values >13.9 mmol/l (r=0.72), but was weakly correlated with the percentage of glucose values <3.9 mmol/l (r=-0.39) or <3.0 mmol/l (r=-0.21). The median percentage of glucose values <3.0 mmol/l was <1.2% (<20 min/day) for all HbA_1c -based groups, but the median percentage of values >13.9 mmol/l varied from 2.5% (0.6 h/day) to 27.8% (6.7 h/day) in the lowest and highest HbA_1c groups, respectively. More than 90% of participants with either <2% of glucose values >13.9 mmol/l, mean glucose <7.8 mmol/l, or time in range >80% had HbA_1c levels ≤53 mmol/mol (≤7.0%). For participants with HbA_1c ≥64 mmol/mol (≥8.0%), the median time in range was 44%, with 90% of participants having a time in range of <59%.

The associations shown in the present study suggest that continuous glucose monitoring-derived metrics may help guide diabetes therapy intensification efforts in an HbA_1c -independent manner.