Discrepancies between Glycosylated Hemoglobin and Fasting Plasma Glucose for Diagnosing Impaired Fasting Glucose and Diabetes Mellitus in Korean Youth and Young Adults

Abstract

Background: Glycosylated hemoglobin (HbA1c) has been recommended as a diagnostic test for prediabetes and diabetes. Here, we evaluated the level of agreement between diagnoses based on fasting plasma glucose (FPG) versus HbA1c levels and determined optimal HbA1c cutoff values for these diseases in youth and young adults.

Methods: The study included 7,332 subjects (n=4,129, aged 10 to 19 years in youth group; and n=3,203 aged 20 to 29 years in young adult group) from the 2011 to 2016 Korea National Health and Nutrition Examination Survey. Prediabetes and diabetes were defined as 100 to 125 mg/dL (impaired fasting glucose [IFG]) and ≥126 mg/dL for FPG (diabetes mellitus [DM] by FPG [DM_FPG]), and 5.7% to 6.4% and ≥6.5% for HbA1c, respectively.

Results: In the youth group, 32.5% with IFG had an HbA1c level of 5.7% to 6.4%, and 72.2% with DM_FPG had an HbA1c ≥6.5%. In the young adult group, 27.5% with IFG had an HbA1c level of 5.7% to 6.4%, and 66.6% with DM_FPG had an HbA1c ≥6.5%. Kappa coefficients for agreement between the FPG and HbA1c results were 0.12 for the youth group and 0.19 for the young adult group. In receiver operating characteristic curve analysis, the optimal HbA1c cutoff for IFG and DM_FPG were 5.6% and 5.9% in youths and 5.5% and 5.8% in young adults, respectively.

Conclusion: Usefulness of HbA1c for diagnosis of IFG and DM_FPG in Koreans aged <30 years remains to be determined due to discrepancies between the results of glucose- and HbA1c-based tests. Additional testing might be warranted at lower HbA1c levels to detect IFG and DM_FPG in this age group.

Keywords: Adolescent; Blood glucose; Diabetes mellitus; Diagnosis; Glycated hemoglobin A; Prediabetic state; Young adult.

Fig. 1. Flow chart for the selection of study participants. KNHANES, Korea National Health and Nutrition Examination Survey; HbA1c, glycosylated hemoglobin.

Fig. 2. Receiver operator characteristic curves for detection of (A) impaired fasting glucose (fasting plasma glucose ≥100 mg/dL) and (B) diabetes mellitus (fasting plasma glucose ≥126 mg/dL) according to glycosylated hemoglobin levels. (A) The area under the curve (AUC) (95% confidence interval [CI]) for impaired fasting glucose was 0.649 (95% CI, 0.648 to 0.650) in the youth group (10 to 19 years of age) and 0.700 (95% CI, 0.699 to 0.701) in the young adult group (20 to 29 years of age) (P<0.001). (B) The AUC (95% CI) for diabetes mellitus was 0.996 (95% CI, 0.996 to 0.996) in the youth group and 0.962 (95% CI, 0.962 to 0.963) in the young adult group (P<0.001).