Article Text

Original research
Concordance between fasting plasma glucose and HbA1c in the diagnosis of diabetes in black South African adults: a cross-sectional study
  1. Alisha N Wade1,
  2. Nigel J Crowther2,3,
  3. Shafika Abrahams-Gessel4,
  4. Lisa Berkman5,
  5. Jaya A George2,3,
  6. F Xavier Gómez-Olivé1,
  7. Jennifer Manne-Goehler6,
  8. Joshua A Salomon7,
  9. Ryan G Wagner1,
  10. Thomas A Gaziano4,8,
  11. Stephen M Tollman1,9,10,
  12. Anne R Cappola11
  1. 1MRC/Wits Rural Public Health and Health Transitions Research Unit, School of Public Health, University of the Witwatersrand, Johannesburg, South Africa
  2. 2Department of Chemical Pathology, University of the Witwatersrand, Johannesburg, South Africa
  3. 3Department of Chemical Pathology, National Health Laboratory Service, Johannesburg, South Africa
  4. 4Centre for Health Decision Science, Harvard University T H Chan School of Public Health, Boston, Massachusetts, USA
  5. 5Harvard Centre for Population and Development Studies, Harvard University T H Chan School of Public Health, Boston, Massachusetts, USA
  6. 6Division of Infectious Diseases, Massachusetts General Hospital, Boston, Massachusetts, USA
  7. 7Centre for Health Policy, Stanford University, Stanford, California, USA
  8. 8Division of Cardiovascular Medicine, Brigham and Women’s Hospital, Boston, Massachusetts, USA
  9. 9INDEPTH Network, Accra, Ghana
  10. 10Umeå Centre for Global Health Research, Division of Epidemiology and Global Health, Department of Public Health and Clinical Medicine, Umeå University, Umeå, Sweden
  11. 11Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA
  1. Correspondence to Dr Alisha N Wade; Alisha.wade{at}wits.ac.za

Abstract

Objectives We investigated concordance between haemoglobin A1c (HbA1c)-defined diabetes and fasting plasma glucose (FPG)-defined diabetes in a black South African population with a high prevalence of obesity.

Design Cross-sectional study.

Setting Rural South African population-based cohort.

Participants 765 black individuals aged 40–70 years and with no history of diabetes.

Primary and secondary outcome measures The primary outcome measure was concordance between HbA1c-defined diabetes and FPG-defined diabetes. Secondary outcome measures were differences in anthropometric characteristics, fat distribution and insulin resistance (measured using Homoeostatic Model Assessment of Insulin Resistance (HOMA-IR)) between those with concordant and discordant HbA1c/FPG classifications and predictors of HbA1c variance.

Results The prevalence of HbA1c-defined diabetes was four times the prevalence of FPG-defined diabetes (17.5% vs 4.2%). Classification was discordant in 15.7% of participants, with 111 individuals (14.5%) having HbA1c-only diabetes (kappa 0.23; 95% CI 0.14 to 0.31). Median body mass index, waist and hip circumference, waist-to-hip ratio, subcutaneous adipose tissue and HOMA-IR in participants with HbA1c-only diabetes were similar to those in participants who were normoglycaemic by both biomarkers and significantly lower than in participants with diabetes by both biomarkers (p<0.05). HOMA-IR and fat distribution explained additional HbA1c variance beyond glucose and age only in women.

Conclusions Concordance was poor between HbA1c and FPG in diagnosis of diabetes in black South Africans, and participants with HbA1c-only diabetes phenotypically resembled normoglycaemic participants. Further work is necessary to determine which of these parameters better predicts diabetes-related morbidities in this population and whether a population-specific HbA1c threshold is necessary.

  • general diabetes
  • epidemiology
  • international health services
  • public health

Data availability statement

Data are available in a public, open access repository. Data are available on reasonable request. The HAALSI baseline data are publicly available at the Harvard Centre for Population and Development Studies (HCPDS) programme website (www.haalsi.org). Data are also accessible through the Inter-university Consortium for Political and Social Research (ICPSR) at the University of Michigan (www.icpsr.umich.edu) and the INDEPTH Data Repository (http://www.indepth-ishare.org/index.php/catalog/113). Data from the AWI-Gen study is available on request to the AWI-Gen Data and Biospecimen Access Committee (michele.ramsay@wits.ac.za). Additional data are available on request from Alisha Wade (alisha.wade@wits.ac.za), the principal investigator of this nested study.

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Data availability statement

Data are available in a public, open access repository. Data are available on reasonable request. The HAALSI baseline data are publicly available at the Harvard Centre for Population and Development Studies (HCPDS) programme website (www.haalsi.org). Data are also accessible through the Inter-university Consortium for Political and Social Research (ICPSR) at the University of Michigan (www.icpsr.umich.edu) and the INDEPTH Data Repository (http://www.indepth-ishare.org/index.php/catalog/113). Data from the AWI-Gen study is available on request to the AWI-Gen Data and Biospecimen Access Committee (michele.ramsay@wits.ac.za). Additional data are available on request from Alisha Wade (alisha.wade@wits.ac.za), the principal investigator of this nested study.

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Footnotes

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  • Contributors ANW, NJC, SA-G, LB, FXG-O, JAS, RGW, TAG and SMT were involved in design and data collection for the HAALSI and AWI-Gen studies. ANW and ARC designed this analysis and ANW performed the statistical analysis. ANW and ARC wrote the first draft of the manuscript. ANW, NJC, SA-G, LB, JAG, FXG-O, JM-G, JAS, RGW, TAG, SMT and ARC critically revised the manuscript and approved the final version. ANW is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. ANW, NJC, SA-G, LB, JAG, FXG-O, JM-G, JAS, RGW, TAG, SMT and ARC have reviewed the final version of this manuscript and agree to be accountable for all aspects of the work.

  • Funding The AWI-Gen Collaborative Centre is funded by the National Human Genome Research Institute (NHGRI), Office of the Director (OD), the Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD), the National Institute of Environmental Health Sciences (NIEHS), the Office of AIDS Research (OAR) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) of the National Institutes of Health (NIH) under award number U54HG006938 and its supplements, as part of the H3Africa Consortium as well as by the Department of Science and Innovation, South Africa, award number DST/CON 0056/2014, and by the African Partnership for Chronic Disease Research. The HAALSI study was funded by the National Institute on Aging (P01 AG041710). The MRC/Wits Rural Public Health and Health Transitions Research Unit and Agincourt Health and Socio-Demographic Surveillance System, a node of the South African Population Research Infrastructure Network (SAPRIN), is supported by the Department of Science and Innovation, South Africa, the University of the Witwatersrand, and the Medical Research Council, South Africa, and previously the Wellcome Trust, UK (grants 058893/Z/99/A; 069683/Z/02/Z; 085477/Z/08/Z; 085477/B/08/Z). ANW is supported by the Fogarty International Centre, National Institutes of Health under award number K43TW010698 and ARC is supported by the National Institute on Ageing, National Institutes of Health under award K24AG042765. JM-G is supported by grant number T32 AI007433 from the National Institute of Allergy and Infectious Diseases.

  • Disclaimer This paper describes the views of the authors and does not necessarily represent the official views of the National Institutes of Health (USA), the South African Department of Science and Innovation or by the South African Medical Research Council who funded this research. The funders had no role in study design, data collection, analysis and interpretation, report writing or the decision to submit this article for publication.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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