Serum insulin-like growth factor-I (IGF-I) reference ranges for chemiluminescence assay in childhood and adolescence. Data from a population of in- and out-patients.

BACKGROUND: Insulin-like growth factor I (IGF-I) measurement is widely used for the diagnosis of disorders of GH secretion and sensitivity, and for monitoring of both GH and IGF-I replacement therapies. However, the lack of appropriate reference values obtained from large and representative samples undermines its practical utility.
OBJECTIVE: To establish IGF-I reference values for a commonly used enzyme-labeled chemiluminescent immunometric assay in a large population of children aged 0 to 18 years.
DESIGN: Cross-sectional analysis of serum IGF-I levels from samples collected in the two major Italian Children's Hospitals. SUBJECTS AND METHODS: IGF-I was measured using a solid-phase, enzyme-labeled chemiluminescent immunometric assay in 24403 children (50.6% girls) aged 0 to 18 years. Quantile regression coupled to multivariable fractional polynomials was used to produce age- and sex-specific reference values. MAIN OUTCOME MEASURE: Age- and sex-specific IGF-I reference values. RESULTS AND
CONCLUSION: Reference values for immunometric assay of IGF-I were produced in a large sample of children and adolescents. Prediction equations were provided to automatize their calculations.