Significance of Plasma C-peptide in Obese African American Adolescents

Background C-peptide blood levels can indicate whether or not a person is producing insulin and roughly how much. C-peptide is secreted as a byproduct of the biosynthesis of insulin from proinsulin. C-peptide has proposed biological activity and a well-established diagnostic value. The significance of C-peptide concentration in the plasma and urine in the pediatric population needs further delineation. Aim: To determine the significance of plasma C-peptide in obese African American adolescents with mild insulin resistance but no evidence of diabetes. Methods This study included 19 African American adolescents with body mass index (BMI) in at least the 85th percentile evaluated with anthropometric measurements, Homeostatic Model Assessment-Insulin Resistance (HOMA-IR) score, and oral glucose tolerance test (OGTT), and 24-hour urine collections. The study also included an age-matched control group of 15 healthy African American adolescent controls and were not subjected for OGTT. The correlation among BMI, fasting plasma C-peptide concentrations, and 24-hour-urine C-peptide concentrations was calculated, t Tests were conducted to compare plasma C-peptide and 24-hour-urine C-peptide concentrations for the test group and controls. Results Mean HOMA score (3.96 ± 1.84) signified mild insulin resistance among the adolescent test group. The test subjects exhibited adequate glucose tolerance (glucose range, 89.4-122.5 mg/dL) during the OGTT. A significant positive relationship was observed between BMI and fasting plasma C-peptide concentration in the control group ( r = 0.537) but not the test group ( r = 0.335). An insignificant positive relationship was exhibited between BMI and 24-hour-urine C-peptide concentration in the test group ( r = 0.150) and controls ( r = 0.254). Conclusions The positive relationship among BMI, plasma C-peptide, and urine C-peptide is worth further evaluation in studies conducting multiple rounds of OGTT with a larger sample of pediatric subjects. The potential diagnostic value of C-peptide may facilitate early detection of insulin resistance in the pediatric population.