Reference values for serum levels of insulin-like growth factor-I and insulin-like growth factor binding protein-3 in Korean children and adolescents

Objective: Measurements of serum insulin-like growth factor-I (IGF-I) and IGF binding protein-3 (IGFBP-3) are utilized in the diagnostic work-up and clinical management of children with growth disorders. We designed this study to establish the reference values of serum IGF-I and IGFBP-3 levels according to age, sex and pubertal stage in Korean children and adolescents. Methods: For the study, 1378 healthy Korean children and adolescents aged 0 to 17. years (722 boys, 656 girls) were randomly selected. Blood samples were collected, and the stored sera were assayed for IGF-I and IGFBP-3 using immunoradiometric assay (IRMA, Immunotech). The R 2.8.1 program (Bell Laboratories) was used to generate reference percentile curves for IGF-I and IGFBP-3 according to age, sex, and pubertal stage. Results: Serum IGFBP-3 level was higher in girls compared to that in boys of the same ages throughout the pubertal period, whereas IGF-I was only higher for girls younger than 13. years of age. Serum levels of IGF-I and IGFBP-3 increased steadily with age in the prepubertal stage, followed by a progressive decline thereafter. Peak levels of serum IGF-I and IGFBP-3 were observed two years earlier in girls compared to those in boys (13 vs. 15. years of age, respectively). Serum IGF-I and IGFBP-3 concentrations were highest at Tanner stage IV in boys and girls, with a subsequent decline. Conclusions: Our reference value model based on age, sex, and pubertal stage can improve the diagnostic utility of IGF-1 and IGFBP-3 levels in the evaluation and management of Korean children and adolescents with growth disorders.