title: Hemoglobin A1c measurements over nearly two decades: sustaining comparable values throughout the Diabetes Control and Complications Trial and the Epidemiology of Diabetes Interventions and Complications study.
abstract: BACKGROUND
  Clinical trials require assays that provide consistent results during the course of a study. The hemoglobin A1c (HbA1c) assay, a measure of chronic glycemia, is critical to the study of diabetes control and complications.
  
  
  METHODS
  The Diabetes Control and Complications Trial (DCCT) and its follow-up study, the Epidemiology of Diabetes Interventions and Complications (EDIC), required 20 years of consistent HbA1c results, measured by three different ion-exchange HPLC procedures. To maintain and document consistent HbA1c results measured in the DCCT and EDIC Central Biochemistry Laboratory, a backup laboratory used frozen hemolysates as long-term calibrators and a HPLC method with a single lot of Bio-Rex 70 resin.
  
  
  RESULTS
  Over 20 years, long-term quality-control values have remained constant. Four studies of nondiabetic ranges produced nearly identical values [mean (SD), 5.1 (0.5)%, 4.9 (0.3)%, 5.0 (0.4)%, and 5.0 (0.3)%].
  
  
  CONCLUSIONS
  The overall consistency of the HbA1c assays during the 20-year course of the DCCT and EDIC has been critical in establishing the benefits of intensive therapy and in understanding the relationship between long-term glycemia and the development and progression of the complications of diabetes.
authors.affiliation: Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN 55454, USA. steff001@umn.edu
authors.forename: Michael
authors.initials: M
authors.lastname: Steffes
authors.forename: Patricia
authors.initials: P
authors.lastname: Cleary
authors.forename: David
authors.initials: D
authors.lastname: Goldstein
authors.forename: Randie
authors.initials: R
authors.lastname: Little
authors.forename: Hsiao-Mei
authors.initials: HM
authors.lastname: Wiedmeyer
authors.forename: Curt
authors.initials: C
authors.lastname: Rohlfing
authors.forename: Jack
authors.initials: J
authors.lastname: England
authors.forename: Jean
authors.initials: J
authors.lastname: Bucksa
authors.forename: Maren
authors.initials: M
authors.lastname: Nowicki
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000592:standards; D019411:Clinical Laboratory Techniques / Q000592:standards*; D002986:Clinical Trials as Topic; D048909:Diabetes Complications / Q000175:diagnosis / Q000517:prevention & control; D003920:Diabetes Mellitus / Q000175:diagnosis* / Q000453:epidemiology / Q000517:prevention & control; D006442:Glycated Hemoglobin / Q000032:analysis* / Q000592:standards; D006801:Humans; D007753:Laboratories / Q000592:standards; D011786:Quality Control; D012015:Reference Standards; D013995:Time
chemical_list: D006442:Glycated Hemoglobin