title: Alternative indices of glucose homeostasis as biochemical diagnostic tests for abnormal glucose tolerance in an African setting.
abstract: Accurate diabetes diagnosis is important in Africa, where rates are increasing, and the disease largely undiagnosed. The cumbersome oral glucose tolerance test (OGTT) remains the reference standard, while alternative diagnostic methods are not yet established in Africans. We assessed the ability of fasting plasma glucose (FPG), HbA1c and fructosamine, to diagnose OGTT-based abnormal glucose tolerance in mixed-ancestry South Africans.
  
  
  
  Mixed-ancestry adults, residing in Cape Town were examined between February and November 2015. OGTT values were used to classify glucose tolerance status as: screen-detected diabetes, prediabetes, dysglycaemia (combination of diabetes and prediabetes) and normal glucose tolerance.
  
  
  
  Of the 793 participants included, 65 (8.2%) had screen-detected diabetes, 157 (19.8%) prediabetes and 571 (72.0%) normal glucose tolerance. Correlations of FPG and 2-h glucose with HbA1c (r=0.51 and 0.52) were higher than those with fructosamine (0.34 and 0.30), both p<0.0001. The highest c-statistic for the prediction of abnormal glucose tolerance was recorded with 2-h glucose [c-statistic=0.997 (screen-detected diabetes), 0.979 (prediabetes) and 0.984 (dysglycaemia)] and the lowest with fructosamine (0.865, 0.596 and 0.677). At recommended or data-specific optimal cut-offs, no combination of FPG, HbA1c and fructosamine did better than 2-h glucose, while FPG was better than HbA1c and fructosamine on a range of performance measures.
  
  
  
  Abnormal glucose tolerance in this population is overwhelmingly expressed through 2-h glucose's abnormalities; and no combination of FPG, HbA1c and fructosamine was effective at accurately discriminating OGTT-defined abnormal glucose tolerance. Tested non-glucose based strategies are unreliable alternatives to OGTT for dysglycaemia diagnosis in this population.
authors.affiliation: Non-Communicable Diseases Research Unit, South African Medical Research Council, Cape Town, South Africa; Department of Medicine, University of Cape Town, Cape Town, South Africa. Electronic address: andre.kengne@mrc.ac.za.
authors.forename: Andre Pascal
authors.initials: AP
authors.lastname: Kengne
authors.affiliation: Division of Chemical Pathology, Faculty of Medicine and Health Sciences, National Health Laboratory Service (NHLS), University of Stellenbosch, Cape Town, South Africa.
authors.forename: Rajiv T
authors.initials: RT
authors.lastname: Erasmus
authors.affiliation: Department of Medicine, University of Cape Town, Cape Town, South Africa; Chronic Disease Initiative for Africa (CDIA), University of Cape Town, Cape Town, South Africa.
authors.forename: Naomi S
authors.initials: NS
authors.lastname: Levitt
authors.affiliation: Faculty of Health and Wellness Sciences, Cape Peninsula University of Technology, Cape Town, South Africa.
authors.forename: Tandi E
authors.initials: TE
authors.lastname: Matsha
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D001786:Blood Glucose / Q000378:metabolism*; D003430:Cross-Sectional Studies; D003920:Diabetes Mellitus / Q000097:blood / Q000175:diagnosis* / Q000208:ethnology; D005215:Fasting / Q000097:blood*; D005260:Female; D019270:Fructosamine / Q000097:blood*; D018149:Glucose Intolerance / Q000097:blood / Q000175:diagnosis* / Q000208:ethnology; D005951:Glucose Tolerance Test; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006706:Homeostasis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011236:Prediabetic State / Q000097:blood / Q000175:diagnosis / Q000208:ethnology; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D013019:South Africa / Q000453:epidemiology
chemical_list: D015415:Biomarkers; D001786:Blood Glucose; D019270:Fructosamine; D006442:Glycated Hemoglobin; C517652:hemoglobin A1c protein, human
keywords: Diagnosis; Fructosamine; Glucose tolerance; HbA1c; Plasma glucose