HbA1c cutoff for prediabetes and diabetes based on oral glucose tolerance test in obese children and adolescents

Background: Oral glucose tolerance test (OGTT) is a traditional diagnostic tool for diabetes. Hemoglobin A1c (HbA1c) is an alternative method used in adults; however, its application in youths has been controversial. We evaluated the diagnostic performance of HbA1c and determined optimal cutoff points for detecting prediabetes and diabetes in youth. Methods: This retrospective study included 389 obese children (217 boys, 55.8%) who had undergone simultaneous OGTT and HbA1c testing at six hospitals, Korea, between 2010 and 2016. Subjects were diagnosed with diabetes (fasting glucose ≥ 7.0 mmol/L; 2-hour glucose ≥ 11.1 mmol/L) or prediabetes (fasting glucose 5.6-6.9 mmol/L; 2-hour glucose 7.8-11.0 mmol/L). The diagnostic performance of HbA1c for prediabetes and diabetes was determined using the area under the receiver operating characteristic curve (AUC). Results: At diagnosis, 197 (50.6%) subjects had normoglycemia, 121 (31.1%) had prediabetes, and 71 (18.3%) had diabetes. The kappa coefficient for agreement between OGTT and HbA1c was 0.464. The optimal HbA1c cutoff points were 5.8% (AUC, 0.795; a sensitivity of 64.1% and a specificity of 83.8%) for prediabetes and 6.2% (AUC, 0.972; a sensitivity of 91.5% and a specificity of 93.7%) for diabetes. When HbA1c (≥ 6.2%) and 2-hour glucose level were used to diagnose diabetes, 100% were detected. Conclusion: Pediatric criteria for HbA1c remain unclear, therefore, we recommend the combination of fasting and 2-hour glucose levels, in addition to HbA1c, in the diagnosis of childhood prediabetes and diabetes.