Introduction.
Fasting glucose (FG) is part of the Adult Treatment Panel III (ATP III) criteria for defining the metabolic syndrome (MetS). Glycated hemoglobin (HbA1c) is a measure of 2-3 month endogenous glucose exposure and is now recommended for diabetes diagnosis and screening for high-risk individuals. The aim of this study was to evaluate if replacing FG with HbA1c to define MetS improves prediction of incident coronary heart disease (CHD) in the Atherosclerosis Risk in Communities (ARIC) cohort.
Methods.
We included 11,194 ARIC participants without diabetes (based on diagnosis, medication use, FG ≥126 mg/dL, or HbA1c ≥6.5%) or prevalent CHD at baseline (1990-92). Cox proportional hazards models (adjusted for age, race, and study center) were used to compare the association between MetS defined using HbA1c (5.7-6.4%) or FG (100-125 mg/dL, based on ATP III guidelines) and risk of CHD (defined by myocardial infarction or fatal CHD, event data available through 2009).
Results.
Study participants had a mean age at baseline of 57 years, 43% were male, and 79% were white; median follow-up time was 16 years. Thirty-four percent of the study population had both normal FG (<100 mg/dL) and HbA1c (<5.7%), 37% had elevated FG and normal HbA1c, 4% had normal FG and elevated HbA1c, and 25% had both elevated FG (100-125 mg/dL) and HbA1c (5.7-6.4%). The association of combined FG and HbA1c categories with incident CHD are shown in the Figure. The adjusted hazard ratio predicting for incident CHD from MetS status was 1.43 (95% CI: 1.25-1.63, c-statistic: 0.61) using FG in the definition of MetS and 1.69 (95% CI: 1.48-1.93, c-statistic: 0.62) in the model replacing FG with HbA1c.
Conclusions.
Incorporating HbA1c into the definition of the MetS may help in identifying individuals who should be targeted for aggressive CHD risk factor reduction. Additionally, HbA1c may be useful clinically and in research settings for identifying individuals with MetS in cases where FG measures are not available.
GLYCATED HEMOGLOBIN: A NEW PARADIGM FOR THE METABOLIC SYNDROME?