Beta cell function and insulin sensitivity in youth with early type 1 diabetes from a two-hour 7-sample OGTT


 
 
 The oral minimal model is a widely accepted noninvasive tool to quantify both β-cell responsiveness and insulin sensitivity from glucose, C-peptide and insulin concentrations during a 3-h 9-point oral glucose tolerance test (OGTT). Here, we aimed to validate a 2-h 7-point protocol against the 3-h OGTT and to test how variation in early sampling frequency impacts estimates of β-cell responsiveness and insulin sensitivity.
 
 
 
 We conducted a secondary analysis on 15 lean youth with stage 1 T1D (≥2islet autoantibodies with no dysglycemia) who underwent a 3-h 9-point OGTT. The oral minimal model was used to quantitate β-cell responsiveness (φtotal) and insulin sensitivity (SI), allowing assessment of β-cell function by the disposition index (DI=φtotal × SI). Seven- and 5-point 2-h OGTT protocols were tested against the 3-h 9-point gold standard to determine agreement between estimates of φtotal and its dynamic and static components, SI, and DI across different sampling strategies.
 
 
 
 The 2-h estimates for the disposition index exhibited a strong correlation with 3-h measures (r = 0.975, p < 0.001) with similar results for β-cell responsiveness and insulin sensitivity (r = 0.997 and r = 0.982, p < 0.001, respectively). The agreement of the three estimates between the 7-point 2-h and 9-point 3-h protocols fell within the 95% CI on the Bland-Altman grid with a median difference of 16.9%(-35.3, 32.5), 0.2%(-0.6, 1.3) and 14.9%(-1.4, 28.3) for DI, φtotal and SI. Conversely, the 5-point protocol did not provide reliable estimates of φ dynamic and static components.
 
 
 
 The 2-h 7-point OGTT is reliable in subjects with Stage 1 T1D for assessment of β-cell responsiveness, insulin sensitivity, and disposition index. Incorporation of these analyses into current 2-h diabetes staging and monitoring OGTTs offers the potential to more accurately quantify risk of progression in the early stages of T1D.
