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Diabetes Technol Ther. 2019 Feb;21(2):81-85. doi: 10.1089/dia.2018.0310. Epub 2018 Dec 21.

The Relationship of Hemoglobin A1C to Time-in-Range in Patients with Diabetes.

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Medical Affairs and Data Science and Informatics, Medtronic Diabetes, Northridge, California.



There has been recent recognition of the limitations of hemoglobin A1C (HbA1C) in describing both short- and long-term glycemic control. Continuous glucose monitoring (CGM) provides robust data about short-term glycemic control and provides metrics such as percent time-in-range (%TIR) that are now routinely reported to describe the change in glycemic control after an intervention in a clinical study or a change in therapy in a patient's care. Recent studies have shown that %TIR may have similar associations with diabetes microvascular complications as does HbA1C. The relationship of %TIR to the long-standing metric of overall glycemic control has not been clearly defined to date.


Articles that report paired HbA1C and %TIR metrics (n = 1137) or HbA1C and frequent self-monitoring of blood glucose (SMBG) (n = 1440) across a wide range of HbA1Cs, technologies, and subject demographics were reviewed to determine the correlation of these metrics.


Selected paired HbA1C and %TIR data from 18 articles were evaluated by linear regression analysis and Pearson's correlation coefficient. There was an excellent correlation between the two (R = -0.84; R2 = 0.71). This relationship did not change after excluding one study that used SMBG or six studies with ≤7 days of CGM. For every absolute 10% change in %TIR, there was a 0.8% (9 mmol/mol) change in HbA1C.


There is a good correlation between HbA1C and %TIR that may permit the transition to %TIR as the preferred metric for determining the outcome of clinical studies, predicting of the risk of diabetes complications, and assessing of an individual patient's glycemic control.


Continuous glucose monitoring.; HbA1C; Time-in-range

[Indexed for MEDLINE]

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