Fasting Plasma Glucose and Hemoglobin A1c in Identifying and Predicting Diabetes

Abstract

OBJECTIVE To compare fasting plasma glucose (FPG) and HbA1c in identifying and predicting type 2 diabetes in a population with high rates of diabetes. RESEARCH DESIGN AND METHODS Diabetes was defined as an FPG level ≥126 mg/dL or an HbA1c level ≥6.5%. Data collected from the baseline and second exams (1989–1995) of the Strong Heart Study were used. RESULTS For cases of diabetes identified by FPG ≥126 mg/dL, using HbA1c ≥6.5% at the initial and 4-year follow-up diabetes screenings (or in identifying incident cases in 4 years) among undiagnosed participants left 46% and 59% of cases of diabetes undetected, respectively, whereas for cases identified by HbA1c ≥6.5%, using FPG ≥126 mg/dL left 11% and 59% unidentified, respectively. Age, waist circumference, urinary albumin-to-creatinine ratio, and baseline FPG and HbA1c levels were common significant risk factors for incident diabetes defined by either FPG or HbA1c; triglyceride levels were significant for diabetes defined by HbA1c alone, and blood pressure and sibling history of diabetes were significant for diabetes defined by FPG alone. Using both the baseline FPG and HbA1c in diabetes prediction identified more people at risk than using either measure alone. CONCLUSIONS Among undiagnosed participants, using HbA1c alone in initial diabetes screening identifies fewer cases of diabetes than FPG, and using either FPG or HbA1c alone cannot effectively identify diabetes in a 4-year periodic successive diabetes screening or incident cases of diabetes in 4 years. Using both criteria may identify more people at risk. The proposed models using the commonly available clinical measures can be applied to assessing the risk of incident diabetes using either criterion.