title: Relationship between glycated haemoglobin levels and mean glucose levels over time.
abstract: OBJECTIVE
  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
  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.
authors.affiliation: Diabetes Center, Department of Biostatistics, Massachusetts General Hospital, 50 Staniford Street, Suite 340, Boston, MA 02114, USA. dnathan@Partners.org
authors.forename: D M
authors.initials: DM
authors.lastname: Nathan
authors.forename: H
authors.initials: H
authors.lastname: Turgeon
authors.forename: S
authors.initials: S
authors.lastname: Regan
mesh_terms: D000328:Adult; D000368:Aged; D001786:Blood Glucose / Q000378:metabolism*; D003922:Diabetes Mellitus, Type 1 / Q000097:blood*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood*; D005260:Female; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D044469:Racial Groups; D012016:Reference Values; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D006442:Glycated Hemoglobin