Agreement and Reliability of Fasted and Oral Glucose Tolerance Test-Derived Indices of Insulin Sensitivity and Beta Cell Function in Boys

Abstract

Assessment of plasma insulin and glucose outcomes is important in paediatric studies aimed at reducing future risk of type 2 diabetes and cardiovascular disease. The aims of this study are to determine the between-method agreement and the day-to-day reliability of fasting and oral glucose tolerance test (OGTT)-derived estimates of insulin sensitivity and β-cell function in healthy boys. Fasting and OGTT assesments of insulin resistance and β-cell function were performed on 28 boys (12.3±2.9 years). Measurements were repeated after 1 week (fasting, n=28) and 1 day (OGTT, n=8). Agreement between estimates of insulin resistance and β-cell function was examined using Pearson's correlation coefficient. Reliability was assessed using change in the mean, Pearson's correlation coefficient, and typical error expressed as a coefficient of variation (CV). The Matsuda index was positively related with QUICKI (r=0.88, P<0.001) and negatively related to HOMA-IR (r=-0.76, P<0.001). The Cederholm index was not significantly related with fasting estimates of insulin resistance (all r<0.40, P>0.05). For reliability, QUICKI had the lowest CV% for the fasting (4.7%) and the Cederholm index for the OGTT (6.4%) estimates. The largest CV% was observed in fasting insulin (30.8%) and insulinogenic index 30' (62.5%). This study highlights differences in between-method agreement and day-to-day reliability for estimates of insulin resistance in youth. The low CV supports the use of the FGIR (fasting) and Cederholm (OGTT) indices in this population.