Reference values for serum levels of insulin-like growth factor (IGF-1) and IGF-binding protein 3 (IGFBP-3) and their ratio in Chinese adolescents

OBJECTIVE: To establish the reference values for serum levels of IGF-1 and IGFBP-3 and their ratio in Chinese adolescents aged 12-19 years. DESIGN AND METHODS: 2102 Chinese adolescents were randomly selected from all secondary schools in Hong Kong with 1734 having IGF-1 and IGFBP-3 levels as measured by automated chemiluminescent assays (IMMULITE 2000). LMS (Lambda-Mu-Sigma) method was used to generate reference percentile curves for IGF-1, IGFBP-3 and their ratio. RESULTS: After excluding participants with abnormal thyroid function, 798 boys and 894 girls were included in the analysis with a mean (+/-SD) age of 15.3 (+/-2.0) and 15.7 years (+/-2.0), respectively. Both serum IGF-1 and IGFBP-3 levels tended to be higher in girls than boys before the age of 16. In boys, there was progressive decline in IGF-1 after a pubertal peak at the age of 13-14. In girls, there was a similar decline after the age of 12. In both boys and girls, there was progressive age-dependent decline in IGFBP-3 after the age of 15-16. The pattern of changes for IGF-1/IGFBP-3 ratio was similar to that of the IGF-1 levels. CONCLUSIONS: These reference values of IGF-1 and IGFBP-3 in healthy adolescents should facilitate the clinical management of adolescents with GH-IGF axis disorders.