title: The relationship between {beta}-cell function and glycated hemoglobin: results from the veterans administration genetic epidemiology study.
abstract: OBJECTIVE
  The study objective was to assess the relationship between β-cell function and HbA(1c).
  
  
  METHODS
  A total of 522 Mexican American subjects participated in this study. Each subject received a 75-g oral glucose tolerance test (OGTT) after a 10- to 12-h overnight fast. Insulin sensitivity was assessed with the Matsuda index. Insulin secretory rate was quantitated from deconvolution of the plasma C-peptide concentration. β-Cell function was assessed with the insulin secretion/insulin resistance (IS/IR) (disposition) index and was related to the level of HbA(1c).
  
  
  RESULTS
  At HbA(1c) levels <5.5%, both the Matsuda index of insulin sensitivity and IS/IR index were constant. However, as the HbA(1c) increased >5.5%, there was a precipitous decrease in both the Matsuda index and the IS/IR index. Subjects with HbA(1c) = 6.0-6.4% had a 44 and 74% decrease in the Matsuda index and the IS/IR index, respectively, compared with subjects with HbA(1c) <5.5% (P < 0.01 for both indices). Subjects with normal glucose tolerance and HbA(1c) <5.7% had β-cell function comparable to that of subjects with normal glucose tolerance with HbA(1c) = 5.7-6.4%. However, subjects with impaired fasting glucose or impaired glucose tolerance had a marked decrease in β-cell function independent of their HbA(1c) level.
  
  
  CONCLUSIONS
  The results of the current study demonstrate that in Mexican Americans, as HbA(1c) increases >6.0%, both insulin sensitivity and β-cell function decrease markedly. Performing an OGTT is pivotal for accurate identification of subjects with impaired β-cell function.
authors.affiliation: Division of Diabetes, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA.
authors.forename: Mustafa
authors.initials: M
authors.lastname: Kanat
authors.forename: Diedre
authors.initials: D
authors.lastname: Winnier
authors.forename: Luke
authors.initials: L
authors.lastname: Norton
authors.forename: Nazik
authors.initials: N
authors.lastname: Arar
authors.forename: Chris
authors.initials: C
authors.lastname: Jenkinson
authors.forename: Ralph A
authors.initials: RA
authors.lastname: Defronzo
authors.forename: Muhammad A
authors.initials: MA
authors.lastname: Abdul-Ghani
mesh_terms: D005260:Female; D005951:Glucose Tolerance Test; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000502:physiology; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D014481:United States
chemical_list: D006442:Glycated Hemoglobin; D007328:Insulin