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

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


Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.

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

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Blood Glucose / analysis*
  • Blood Glucose Self-Monitoring
  • Child
  • Diabetes Mellitus, Type 1 / blood*
  • Diabetes Mellitus, Type 1 / drug therapy
  • Diabetes Mellitus, Type 2 / blood*
  • Diabetes Mellitus, Type 2 / drug therapy
  • Female
  • Glycated Hemoglobin A / analysis*
  • Humans
  • Hypoglycemic Agents / therapeutic use
  • Insulin / therapeutic use
  • Insulin Infusion Systems
  • Male
  • Middle Aged
  • Young Adult


  • Blood Glucose
  • Glycated Hemoglobin A
  • Hypoglycemic Agents
  • Insulin
  • hemoglobin A1c protein, human