Objective: The aim of this study was to evaluate HbA(1c) as an alternative criterion for impaired glucose tolerance (IGT) or type 1 diabetes (T1D) in high-risk subjects <21 years of age.
Research design and methods: Subjects <21 years of age who participated in the prospective DPT-1, TEDDY, TRIGR, and Type 1 Diabetes TrialNet Natural History (TrialNet) studies and had an HbA(1c) within 90 days of an OGTT with a 2-h plasma glucose (2-hPG) measure were included. An OGTT of 140-199 mg/dL defined IGT, and an OGTT with 2-hPG ≥200 mg/dL or fasting plasma glucose ≥126 mg/dL defined diabetes. HbA(1c) ≥5.7% defined IGT, and HbA(1c) ≥ 6.5% defined diabetes. Receiver-operating characteristic curve analysis was used to assess diagnostic accuracy of HbA(1c) compared with OGTT.
Results: There were 587 subjects from DPT-1, 884 from TrialNet, 91 from TEDDY, and 420 from TRIGR. As an indicator for IGT, HbA(1c) sensitivity was very low across the studies (8-42%), and specificity was variable (64-95%). With HbA(1c) ≥6.5% threshold used for T1D diagnosis, the sensitivity was very low and specificity was high (sensitivity and specificity: DPT-1 24 and 98%, TrialNet 28 and 99%, TEDDY 34 and 98%, and TRIGR 33 and 99%, respectively). The positive predictive value of HbA(1c) ≥6.5% for the development of T1D was variable (50-94%) across the four studies.
Conclusions: HbA(1c) ≥6.5% is a specific but not sensitive early indicator for T1D in high-risk subjects <21 years of age diagnosed by OGTT or asymptomatic hyperglycemia. Redefining the HbA(1c) threshold is recommended if used as an alternative criterion in diagnosing T1D.