Fasting Indicators of Insulin Sensitivity: Effects of Ethnicity and Pubertal Status

OBJECTIVE To examine the relationship of fasting indicators of insulin sensitivity with a more invasive measure of insulin sensitivity (frequently sampled intravenous glucose tolerance test [FSIVGTT]) and the effect of Tanner stage and ethnicity on that relationship. RESEARCH DESIGN AND METHODS Data were analyzed from 149 overweight girls (97 Hispanic and 52 African American) who were either in the early stages of maturation defined by Tanner stages 1 or 2 (52 Hispanic and 18 African American) or in the later stages of maturation defined by Tanner stages 4 and 5 (45 Hispanic and 34 African American). Fasting indicators of insulin sensitivity (IS) included fasting insulin and glucose and the homeostasis model assessment of insulin resistance (HOMA-IR). IS was derived from an FSIVGTT with minimal modeling. RESULTS In Tanner stages 1 and 2, all fasting indicators were significantly associated with IS: (fasting insulin: r = -0.67, P < 0.01; HOMA: r = -0.66, P < 0.01) with no significant influence of ethnicity on these relationships. In Tanner stages 4 and 5, however, all fasting indicators were associated with IS in African American girls (fasting insulin: r = -0.55, P < 0.01; HOMA: r = -0.47, P < 0.01), but none of the indicators were significantly associated with IS in Hispanic girls. CONCLUSIONS Fasting indicators were reflective of IS for girls in Tanner stages 1 and 2, regardless of ethnicity and may provide a clinical measure of future risk for type 2 diabetes. In the latter stages of maturation, however, more invasive measures are warranted to adequately determine IS in clinical practice.