"Mind the gap please…": estimated vs. measured Ac from continuous measurement of interstitial glucose over a 3-month period in patients with type 1 diabetes.

: Glycated hemoglobin (A) is the measurement of choice to estimate the glycemic exposure over the last 3 months prior to sampling. The Free Style Libre® is a continuous glucose monitoring device which provides an estimated A (eA1c) from average interstitial glucose using Nathan's ADAG equation. The objective of this study was to compare eA1c and A in type 1 diabetes patients (T1D) over a period of 3 months.: Data were collected from patient charts between July 2016 and October 2017. 3-months recordings with >70% of data available were analyzed. eA1c was recorded at each visit and the corresponding A value measured by high performance liquid chromatography in a single reference lab.: A total of 344 reports from 170 T1D were studied, 3 categories were identified: eA1c = A: 13% of reports. eA1c > A: 57% of reports, positive difference (eA1c - A) of +0.74 ± 0.5% (P < 0.0001). eA1c < A: 30% of reports, negative difference (eA1c - A) of -0.5 ± 0.3% (P < 0.0001).: eA1c value was generally overestimated compared to measured A in this T1D cohort. This lesser concordance may result from differences in measured glucose source and/or frequency to calculate eA1c compared to ADAG, but also from using the reverse equation which is a source of potential bias. Another explanation could be a different rate of hypoglycemia between groups, or an asymmetric distribution of A1c patients' phenotypes with differential hyper- or hypoglycation intrinsic propensity.