Relationship between glycated haemoglobin levels and mean glucose levels over time

Diabetologia. 2007 Nov;50(11):2239-44. doi: 10.1007/s00125-007-0803-0. Epub 2007 Sep 13.


Aims/hypothesis: HbA(1c), expressed as the percentage of adult haemoglobin that is glycated, is the most widely used measure of chronic glycaemia. Achieving near-normal HbA(1c) levels has been shown to reduce long-term complications and the HbA(1c) assay is recommended to determine whether treatment is adequate and to guide adjustments. However, daily adjustments of therapy are guided by capillary glucose levels (mmol/l). We determined the relationship between an accurate measure of mean glucose levels over time and the HbA(1c) level, and whether HbA(1c) can be expressed in the same units as self-monitoring results.

Methods: Twenty-two participants with diabetes and three non-diabetic participants were included in this longitudinal observational study. Mean glucose levels were measured by continuous glucose monitoring (CGM), which measures interstitial glucose levels every 5 min, for 12 weeks. Capillary measurements were obtained four times per day to confirm the accuracy of CGM. HbA(1c) was measured at baseline and every 4 weeks.

Results: The HbA(1c) results at weeks 8 and 12 correlated strongly (r = 0.90) with the CGM results during the preceding 8 and 12 weeks. A curvilinear (exponential) relationship and a linear regression captured the relationship with similarly high correlations, which allowed transformation of HbA(1c) values to a calculated mean glucose level.

Conclusions and interpretation: HbA(1c) correlates closely with a complete measure of average glycaemia over the preceding 8-12 weeks. The translation of HbA(1c) to an average glucose level for reporting and management purposes is feasible.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Blood Glucose / metabolism*
  • Diabetes Mellitus, Type 1 / blood*
  • Diabetes Mellitus, Type 2 / blood*
  • Female
  • Glycated Hemoglobin / metabolism*
  • Humans
  • Kinetics
  • Male
  • Middle Aged
  • Racial Groups
  • Reference Values
  • Time Factors


  • Blood Glucose
  • Glycated Hemoglobin A