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

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BMJ open. June 17, 2021; 11 (6): e046060. doi: 10.1136 / bmjopen-2020-046060.

ABSTRACT

OBJECTIVES: We investigated the concordance between hemoglobin A1c (HbA1c) defined diabetes and fasting plasma glucose (FPG) defined diabetes in a black South African population with a high obesity prevalence.

DESIGN: cross-sectional study.

SETTING: rural South African population cohort.

PARTICIPANTS: 765 black people aged 40-70 years with no history of diabetes.

PRIMARY AND SECONDARY OUTCOME MEASURES: The primary endpoint was the concordance between HbA1c-defined diabetes and FPG-defined diabetes. Secondary target parameters were differences in anthropometric characteristics, fat distribution and insulin resistance (measured with the homeostatic model of insulin resistance (HOMA-IR)) between persons with a matching and discordant HbA1c / FPG classification and predictors of the HbA1c variance.

RESULTS: The prevalence of HbA1c-defined diabetes was four times higher than that of FPG-defined diabetes (17.5% vs. 4.2%). The classification was inconsistent in 15.7% of the participants, with 111 people (14.5%) only having HbA1c diabetes (kappa 0.23; 95% CI 0.14 to 0.31). The mean 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 with both normoglycemic biomarkers and significantly lower than in participants with diabetes by both biomarkers (p <0.05). HOMA-IR and fat distribution only explained an additional HbA1c variance beyond glucose and age in women.

CONCLUSIONS: The concordance between HbA1c and FPG in diagnosing diabetes in black South Africans was poor, and participants with only HbA1c diabetes were phenotypically similar to normoglycemic participants. More work is needed to determine which of these parameters better predict diabetes-related morbidities in this population and whether a population-specific HbA1c threshold is required.

PMID: 34140342 | DOI: 10.1136 / bmjopen-2020-046060