Diabetes Metab J.  2016 Apr;40(2):118-128. 10.4093/dmj.2016.40.2.118.

Is an Oral Glucose Tolerance Test Still Valid for Diagnosing Diabetes Mellitus?

  • 1Division of Endocrinology and Metabolism, Department of Internal Medicine, Konkuk University School of Medicine, Seoul, Korea. skh2k@kuh.ac.kr
  • 2Department of Internal Medicine, Graduate School of Medicine, Konkuk University, Seoul, Korea.


We evaluated the diagnostic rate of diabetes using fasting plasma glucose (FPG), 2-hour plasma glucose (2h PG) after 75 g oral glucose tolerance test (OGTT), and glycosylated hemoglobin (HbA1c) levels, and we elucidated the pathophysiologic characteristics and risk factors that give rise to diabetes in patients with prediabetes.
The data of 236 patients who had the OGTT at Konkuk University Hospital were analyzed. Fasting, 30, and 120 minutes blood glucose levels and insulin levels were measured. The diagnostic rate of diabetes was assessed using FPG, 2h PG, and HbA1c levels. The clinical data and insulin resistance and secretion evaluations were compared using indexes according to the fasting glucose level.
Among 236 subjects, 97 (41.1%) were diabetics and 102 (43.2%) were prediabetics. The rate of diabetes diagnosis by one of the individual criteria was 56.7%, 53.6%, and 84.5% for FPG, HbA1c, and 2h PG, respectively. When two criteria were used to diagnose diabetes, 72.2% of the diabetic patients were identified by FPG and HbA1c, while 100% were identified by FPG and 2h PG, and 91.7% were identified by 2h PG and HbA1c. The HbA1c cut-off value for 2h PG ≥200 mg/dL was 6.1%, and the FPG cut-off value was 115 mg/dL. In impaired fasting glucose subjects, the HbA1c level, Matsuda index, and insulinogenic index were associated with risk of occurrence of overt diabetes (P<0.01).
This study suggests that performing additional OGTT for patients with FPG ≥110 mg/dL or HbA1c ≥6.1% is helpful to reclassify their glucose tolerance status and evaluate their potential for progressing to overt diabetes.


Diabetes mellitus; Diagnosis; Glucose tolerance test; Prediabetic state

MeSH Terms

Blood Glucose
Diabetes Mellitus*
Glucose Tolerance Test*
Hemoglobin A, Glycosylated
Insulin Resistance
Prediabetic State
Risk Factors
Blood Glucose


  • Fig. 1 The concordance rate between the three diagnostic criteria of diabetes: fasting plasma glucose (FPG) ≥126 mg/dL; 2-hour plasma glucose (2h PG) after 75 g oral glucose tolerance test ≥200 mg/dL; and glycosylated hemoglobin (HbA1c) ≥6.5%.

  • Fig. 2 Receiver operating characteristic (ROC) curve of (A, B) glycosylated hemoglobin (HbA1c) and (C,D) fasting plasma glucose (FPG) levels for the diagnosis of diabetes with criteria of FPG ≥126 mg/dL or (E, F) 2-hour plasma glucose (2h PG) after 75 g oral glucose tolerance test ≥200 mg/dL or HbA1c ≥6.5%. AUC, area under the curve.

Cited by  1 articles

HbA1c Cutoff for Prediabetes and Diabetes Based on Oral Glucose Tolerance Test in Obese Children and Adolescents
Hyo-Kyoung Nam, Won Kyoung Cho, Jae Hyun Kim, Young-Jun Rhie, Sochung Chung, Kee-Hyoung Lee, Byung-Kyu Suh
J Korean Med Sci. 2018;33(12):.    doi: 10.3346/jkms.2018.33.e93.


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