Pediatric Continuous Reference Intervals of Serum Insulin-like Growth Factor 1 Levels in a Healthy Chinese Children Population-Based on PRINCE Study

Objectives: We aimed to establish age- and sex-dependent reference intervals for insulin-like growth factor 1 (IGF-1) based on the measurements of healthy Chinese children from the pediatric reference intervals in China study and to investigate whether body mass index (BMI) and height affect IGF-1 levels. Methods: A total of 3753 individuals with eligible blood specimens resampled from the pediatric reference intervals in China population were enrolled as reference individuals. IGF-1 levels were measured using a chemiluminescent immunoassay kit. The lower limit and upper limit values of the reference individuals were calculated by defining the 2.5th and 97.5th percentiles. The skewnessmedian-coefficient of variation method was used to calculate the standard deviation score (SDS) of serum IGF-1, and cubic spline curves were applied to depict a smoothed curve for each age- and sexspecific stratification of the L, M, and S parameters. Results: Serum IGF-1 levels increased with age from the age of 1 year, peaking at around the age of 13 years in girls and 15 years in boys and then began to decline (both P <.001). Before 14 years, IGF-1 levels were higher in girls than in boys at the same age, and the difference was statistically significant (P < .05), but there was no significant difference in the IGF-1 levels between girls and boys aged 14 to 16 and 18 years. The Spearman correlation coefficients of height SDS, weight SDS, and BMI SDS with IGF-1 SDS were 0.29, 0.33, and 0.20, respectively (P < .001). Conclusion: This study established age- and sex-specific normative IGF-1 data for Chinese children and adolescents between the ages of 1 and 19 years. The BMI and height SDS had no effect on IGF-1 levels in healthy children.