874-P: Variation of Measured HbA1c from Predicted HbA1c on Freestyle Libre

Aims/objectives: To explore the variation of the predicted HbA_1c in the Free Style Libre (FSL) flash glucose monitoring from the simultaneous measured laboratory HbA_1c (IFCC) value.

Methods: We included all patients (n=114) with adequate data on FSL download who also had HbA_1c estimation in the biochemistry laboratory as a part of follow-up review after FSL initiation for glycaemia management in diabetes. The date of measured HbA_1c estimation was used in the FSL download to obtain a predicted HbA1c (2 months data download). The difference between the measured HbA_1c and predicted HbA_1c was calculated to obtain the variation between the two.

Results: The measured HbA_1c prior to and post FSL initiation were 68.2±15.1 and 59.9±1.2 mmol/mol respectively, i.e the HbA1c improved by mean 8.3 mmol/mol (std. error 0.99) (P<0.001, paired sample t-test). The mean time duration between the pre and follow-up HbA1c estimations was 5.3±1.9 months. The predicted HbA1c on FSL download at follow-up was 61.8±10.1 mmol/mol. The correlation between the mean blood glucose on FSL and predicted HbA1c was significant (r=0.999) which would be expected as the predicted HbA_1c was calculated from mean glucose in FSL. There was a significant correlation between measured HbA_1c and predicted HbA_1c was (r=0.86, P<0.001) The difference between the measured and predicted HbA_1c was minus 2.3±7.2 mmol/mol with a wide range (minus 35 to +12 mmol/mol) with the difference being clinical significant (>10 mmol/mol difference) in 18.4% of the cohort.

Conclusions: This study confirms the variation of the measured HbA_1c from that predicted from FSL flash glucose download data could be clinically significant in about a fifth of individuals. Variety of factors could contribute to such variation and may have clinical implications while managing individuals with diabetes.