Concordance between fasting plasma glucose and HbA1c in the diagnosis of diabetes in black South African adults: a cross-sectional study

Alisha N Wade; Nigel J Crowther; Shafika Abrahams-Gessel; Lisa Berkman; Jaya A George; F Xavier Gómez-Olivé; Jennifer Manne-Goehler; Joshua A Salomon; Ryan G Wagner; Thomas A Gaziano; Stephen M Tollman; Anne R Cappola

doi:10.1136/bmjopen-2020-046060

Concordance between fasting plasma glucose and HbA_1c in the diagnosis of diabetes in black South African adults: a cross-sectional study

BMJ Open. 2021 Jun 17;11(6):e046060. doi: 10.1136/bmjopen-2020-046060.

Authors

Alisha N Wade¹, Nigel J Crowther^{2

3}, Shafika Abrahams-Gessel⁴, Lisa Berkman⁵, Jaya A George^{2

3}, F Xavier Gómez-Olivé⁶, Jennifer Manne-Goehler⁷, Joshua A Salomon⁸, Ryan G Wagner⁶, Thomas A Gaziano^{4

9}, Stephen M Tollman^{6

10

11}, Anne R Cappola¹²

Affiliations

¹ MRC/Wits Rural Public Health and Health Transitions Research Unit, School of Public Health, University of the Witwatersrand, Johannesburg, South Africa Alisha.wade@wits.ac.za.
² Department of Chemical Pathology, University of the Witwatersrand, Johannesburg, South Africa.
³ Department of Chemical Pathology, National Health Laboratory Service, Johannesburg, South Africa.
⁴ Centre for Health Decision Science, Harvard University T H Chan School of Public Health, Boston, Massachusetts, USA.
⁵ Harvard Centre for Population and Development Studies, Harvard University T H Chan School of Public Health, Boston, Massachusetts, USA.
⁶ MRC/Wits Rural Public Health and Health Transitions Research Unit, School of Public Health, University of the Witwatersrand, Johannesburg, South Africa.
⁷ Division of Infectious Diseases, Massachusetts General Hospital, Boston, Massachusetts, USA.
⁸ Centre for Health Policy, Stanford University, Stanford, California, USA.
⁹ Division of Cardiovascular Medicine, Brigham and Women's Hospital, Boston, Massachusetts, USA.
¹⁰ INDEPTH Network, Accra, Ghana.
¹¹ Umeå Centre for Global Health Research, Division of Epidemiology and Global Health, Department of Public Health and Clinical Medicine, Umeå University, Umeå, Sweden.
¹² Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA.

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 HbA_1c-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 HbA_1c/FPG classifications and predictors of HbA_1c variance.

Results: The prevalence of HbA_1c-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 HbA_1c-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 HbA_1c-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 HbA_1c variance beyond glucose and age only in women.

Conclusions: Concordance was poor between HbA_1c and FPG in diagnosis of diabetes in black South Africans, and participants with HbA_1c-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 HbA_1c threshold is necessary.

Keywords: epidemiology; general diabetes; international health services; public health.

Publication types

Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

MeSH terms

Adult
Black or African American
Blood Glucose
Cross-Sectional Studies
Diabetes Mellitus* / diagnosis
Diabetes Mellitus* / epidemiology
Diabetes Mellitus, Type 2* / diagnosis
Diabetes Mellitus, Type 2* / epidemiology
Fasting
Female
Glycated Hemoglobin / analysis
Humans

Substances

Blood Glucose
Glycated Hemoglobin A

Abstract

Publication types

MeSH terms

Substances

Grants and funding