Comparison between beta-cell function and insulin resistance indexes in prepubertal and pubertal obese children

Several methods have been developed to assess insulin resistance (IR), insulin secretion, and sensitivity: some of them, such as the homeostasis model assessment (HOMA) for IR (HOMA IR) and for insulin secretion (HOMA beta cell) and the quantitative insulin sensitivity check index (QUICKI) are based on fasting levels of glucose (fasting G) and insulin (fasting I); others, such as the pancreatic insulin response to glucose (IRG) and the insulin sensitivity index (ISI) are derived from the glycemic and insulinemic responses to the oral glucose tolerance test (OGTT). The aim of the study was to compare these indexes in a large group of prepubertal and pubertal obese subjects and verify whether the data from fasting samples were enough for evaluating IR and insulin secretion or if OGTT was mandatory. A total of 405 obese subjects (221 boys and 184 girls) was studied. Ninty-three were prepubertal (Tanner stage I), 98 early pubertal (stage II to III) and 214 late pubertal (stage IV to V). In each subject, a 120-minute OGTT was performed, and the glycemic (mean blood glucose [MBG]) and insulinemic (mean serum insulin [MSI]) responses, expressed as AUC/120, as well as IRG and ISI were calculated. The fasting I/fasting G ratio (FIGR), HOMA IR, HOMA beta cell, and QUICKI were then measured. FIGR and HOMA IR increased in both sexes during puberty, but in girls, the increase was already evident from stage I to stage II to III, while in boys, it was evident only from stage II to III to stage IV to V. QUICKI decreased in girls at the onset of puberty and was lower than in boys in stage II to III; on the other hand, HOMA beta cell did not show any variation. IRG increased throughout puberty, although it was higher in boys than in girls in stages II to III and IV to V, while ISI decreased at the onset of puberty in boys; HOMA IR correlated with MSI and IRG, and HOMA beta cell with MSI in pubertal subjects only. In conclusion, the indexes deriving from fasting samples, such as FIGR and HOMA IR, proved to be enough for evaluating IR in prepubertal and pubertal obese subjects, as did QUICKI for insulin sensitivity, However, OGTT is still useful for assessing insulin secretion, because IRG is more sensitive in depicting the pubertal variations of IR than HOMA beta cell.