title: Derivation and validation of an HbA1c optimal cutoff for diagnosing prediabetes in a South African mixed ancestry population.
abstract: BACKGROUND
  Prediabetes compromises impaired fasting glucose and impaired glucose tolerance and is a high risk for future diabetes mellitus and cardiovascular disease. Traditional diagnostic methods involve a fasting sample or oral glucose tolerance test, which is cumbersome, time-consuming and inconvenient. An HbA1c-based approach has been incorporated into new guidelines, but cut-offs may vary and have not been defined for all population groups. We derived and validated HbA1c cut-offs to diagnose prediabetes in mixed ancestry South Africans.
  
  
  METHODS
  Participants were 667 (derivation sample), 234 (validation sample 1) and 674 (validation sample 2) diabetes-free individuals. They underwent standard 2-hour OGTT with HbA1c test. Receiver-operator characteristic curves were used to determine optimal HbA1c cut-off to predict prediabetes.
  
  
  RESULTS
  A total of 27.7% participants in the derivation sample had prediabetes versus 17.5% (validation sample 1) and 15.4% (validation sample 2). The optimal cut-off was 5.75% in all three cohorts with sensitivity and specificity of 64.8% and 60.4% in combined derivation and validation sample 1, and 59.6% and 69.8% in validation sample 2.
  
  
  CONCLUSIONS
  The discriminatory capacity of HbA1c for predicting prediabetes in this population is modest at the derived cut-off. The use of HbA1c alone in this setting may result in an inaccurate diagnosis.
authors.affiliation: Division of Chemical Pathology, National Health Laboratory Service, Tygerberg Hospital, Cape Town, South Africa; University of Stellenbosch, Tygerberg Hospital, Cape Town, South Africa. Electronic address: azemlin@sun.ac.za.
authors.forename: Annalise E
authors.initials: AE
authors.lastname: Zemlin
authors.affiliation: Department of Biomedical Sciences, Cape Peninsula University of Technology, Cape Town, South Africa. Electronic address: matshat@cput.ac.za.
authors.forename: Tandi E
authors.initials: TE
authors.lastname: Matsha
authors.affiliation: Non-Communicable Diseases Research Unit, Medical Research Council, Cape Town, South Africa; University of Cape Town, Cape Town, South Africa. Electronic address: Andre.Kengne@mrc.ac.za.
authors.forename: Andre P
authors.initials: AP
authors.lastname: Kengne
authors.affiliation: Division of Chemical Pathology, National Health Laboratory Service, Tygerberg Hospital, Cape Town, South Africa; University of Stellenbosch, Tygerberg Hospital, Cape Town, South Africa. Electronic address: rte@sun.ac.za.
authors.forename: Rajiv T
authors.initials: RT
authors.lastname: Erasmus
mesh_terms: D005260:Female; D006442:Glycated Hemoglobin / Q000032:analysis*; D006801:Humans; D007118:Immunoassay; D008297:Male; D008875:Middle Aged; D011236:Prediabetic State / Q000097:blood* / Q000175:diagnosis*; D044469:Racial Groups; D013019:South Africa
chemical_list: D006442:Glycated Hemoglobin; C517652:hemoglobin A1c protein, human
keywords: HbA1c; Optimal cut-off; Prediabetes; ROC curve