One-Hour Oral Glucose Tolerance Tests (OGTTs) for the Prediction and Diagnostic Surveillance of Type 1 Diabetes (T1D)

Natural history studies and prevention trials for T1D use 2 hour OGTTs for two main goals: prediction and diagnostic surveillance. Although 2 hour OGTTs are reliable for these purposes, they impose time burdens and costs for research participants and staff. We thus examined whether 1 hour OGTTs are suitable for prediction and diagnostic surveillance. To assess their accuracy for prediction, we developed a 1 hour risk score similar to the Diabetes Prevention Trial-Type 1 Risk Score (DPTRS). The DPTRS utilizes log fasting C-peptide, sums of 30, 60, 90 and 120-min glucose and C-peptide, age, and log BMI. The components are the same for the 1 hour risk score (DPTRS60) and the DPTRS except that 1 hour glucose and C-peptide replace the glucose sum and C-peptide sum. Diabetes Prevention Trial-Type 1 participants were included in the analysis (n=670; age at baseline: 13.8±9.6 years; 56% male; 241 diagnosed with T1D). 1 hour glucose and C-peptide were highly predictive of T1D within the DPTRS60 model, as were log fasting C-peptide, age and log BMI (all p<0.001). The receiver operating characteristic AUC was almost identical for the DPTRS and DPTRS60 (both 0.81, p<0.001). To assess diagnostic surveillance, we sought to identify a 1 hour glucose threshold below which a diagnosis of T1D would be unlikely. Of 162 (among the 241 total) diagnosed by 2 hour OGTTs, only 2 (1.2%) had a 1 hour- glucose <180 mg/dl at diagnosis. Of 172 with a 1 hour glucose <180 mg/dl at baseline who were ultimately diagnosed, only 1 (0.6%) was diagnosed before the 6±3 month window for the next monitoring visit. 568/670 (85%) had a 1 hour glucose <180 mg/dl at baseline. These findings show that 1 hour OGTTs are virtually as predictive of T1D as 2 hour OGTTs. Also, it appears that a 1 hour glucose <180 mg/dl ensures a very low risk for T1D before the next routine monitoring visit. Moreover, most 1 hour glucose values are <180 mg/dl. Accordingly, 1 hour OGTTs can reduce time burdens and costs for the majority of T1D natural history and prevention trial participants.