title: Glucoregulatory function among African Americans and European Americans with normal or pre-diabetic hemoglobin A1c levels.
abstract: OBJECTIVE
  A hemoglobin (Hb) A1c range of 5.7%-6.4% has been recommended for the diagnosis of prediabetes. To determine the significance of such "prediabetic" HbA1c levels, we compared glucoregulatory function in persons with HbA1c levels of 5.7%-6.4% and those with HbA1c<5.7%.
  
  
  METHODS
  We studied 280 nondiabetic adults (142 black, 138 white; mean (±SD) age 44.2±10.6 years). Each subject underwent clinical assessment, blood sampling for HbA1c measurement, and a 75-g oral glucose tolerance test at baseline. Additional assessments during subsequent outpatient visits included insulin sensitivity, using homeostasis model assessment (HOMA)-IR and the hyperinsulinemic euglycemic clamp; insulin secretion, using HOMA-B and frequently samples intravenous glucose tolerance test (FSIVGTT) and disposition index (DI); and measurement of fat mass, using DXA.
  
  
  RESULTS
  Compared to subjects with HbA1c<5.7%, persons with HbA1c levels of 5.7%-6.4% were older, and had higher body mass index (BMI) and insulin secretion but similar insulin sensitivity. When the two groups were matched in age and BMI, persons with HbA1c 5.7%-6.4% were indistinguishable from those with HbA1c <5.7% with regard to all measures of glycemia and glucoregulatory function.
  
  
  CONCLUSIONS
  Unlike glucose-defined prediabetes status, an HbA1c range of 5.7%-6.4% does not reliably identify individuals with impaired insulin action or secretion, the classical defects underlying the pathophysiology of prediabetes. Thus, HbA1c cannot validly replace blood glucose measurement in the diagnosis of prediabetes. If utilized as a screening test due to convenience, aberrant HbA1c values should be corroborated with blood glucose measurement before therapeutic intervention.
authors.affiliation: Division of Endocrinology, Diabetes and Metabolism and General Clinical Research Center, University of Tennessee Health Science Center, Memphis, TN.
authors.forename: Sotonte
authors.initials: S
authors.lastname: Ebenibo
authors.affiliation: Division of Endocrinology, Diabetes and Metabolism and General Clinical Research Center, University of Tennessee Health Science Center, Memphis, TN.
authors.forename: Chimaroke
authors.initials: C
authors.lastname: Edeoga
authors.affiliation: Division of Endocrinology, Diabetes and Metabolism and General Clinical Research Center, University of Tennessee Health Science Center, Memphis, TN.
authors.forename: Jim
authors.initials: J
authors.lastname: Wan
authors.affiliation: Division of Endocrinology, Diabetes and Metabolism and General Clinical Research Center, University of Tennessee Health Science Center, Memphis, TN. Electronic address: sdj@uthsc.edu.
authors.forename: Samuel
authors.initials: S
authors.lastname: Dagogo-Jack
mesh_terms: D000328:Adult; D001741:Black or African American / Q000706:statistics & numerical data*; D000367:Age Factors; D000368:Aged; D015415:Biomarkers / Q000097:blood; D001786:Blood Glucose / Q000378:metabolism*; D015992:Body Mass Index; D003937:Diagnosis, Differential; D005260:Female; D018149:Glucose Intolerance; D005951:Glucose Tolerance Test; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood / Q000378:metabolism; D007333:Insulin Resistance; D000078790:Insulin Secretion; D008297:Male; D008875:Middle Aged; D011236:Prediabetic State / Q000097:blood* / Q000175:diagnosis / Q000208:ethnology* / Q000378:metabolism; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D014481:United States / Q000453:epidemiology; D044465:White People / Q000706:statistics & numerical data*
chemical_list: D015415:Biomarkers; D001786:Blood Glucose; D006442:Glycated Hemoglobin; D007328:Insulin; C517652:hemoglobin A1c protein, human
keywords: A1C; Insulin secretion; Insulin sensitivity; Prediabetes diagnosis; Race/Ethnicity