The Relationships Between Time in Range, Hyperglycemia Metrics, and HbA1c

J Diabetes Sci Technol. 2019 Jul;13(4):614-626. doi: 10.1177/1932296818822496. Epub 2019 Jan 13.


Background: As the use of continuous glucose monitoring (CGM) increases, there is a need to better understand key metrics of time in range 70-180 mg/dL (TIR70-180) and hyperglycemia and how they relate to hemoglobin A1c (A1C).

Methods: Analyses were conducted utilizing datasets from four randomized trials encompassing 545 adults with type 1 diabetes (T1D) who had central-laboratory measurements of A1C. CGM metrics were calculated and compared with each other and A1C cross-sectionally and longitudinally.

Results: Correlations among CGM metrics (TIR70-180, time >180 mg/dL, time >250 mg/dL, mean glucose, area under the curve above 180 mg/dL, high blood glucose index, and time in range 70-140 mg/dL) were typically 0.90 or greater. Correlations of each metric with A1C were lower (absolute values 0.66-0.71 at baseline and 0.73-0.78 at month 6). For a given TIR70-180 percentage, there was a wide range of possible A1C levels that could be associated with that TIR70-180 level. On average, a TIR70-180 of 70% and 50% corresponded with an A1C of approximately 7% and 8%, respectively. There also was considerable spread of change in A1C for a given change in TIR70-180, and vice versa. An increase in TIR70-180 of 10% (2.4 hours per day) corresponded to a decrease in A1C of 0.6%, on average.

Conclusions: In T1D, CGM measures reflecting hyperglycemia (including TIR and mean glucose) are highly correlated with each other but only moderately correlated with A1C. For a given TIR or change in TIR there is a wide range of possible corresponding A1C values.

Keywords: continuous glucose monitoring; glucose time in range; type 1 diabetes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Benchmarking
  • Blood Glucose / analysis*
  • Blood Glucose Self-Monitoring*
  • Cross-Sectional Studies
  • Diabetes Mellitus, Type 1 / blood*
  • Female
  • Glycated Hemoglobin A / analysis*
  • Humans
  • Hyperglycemia / blood*
  • Male
  • Middle Aged
  • Young Adult


  • Blood Glucose
  • Glycated Hemoglobin A
  • hemoglobin A1c protein, human