RESUMEN
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.
Asunto(s)
Pacientes Internos , Factor I del Crecimiento Similar a la Insulina/metabolismo , Pacientes Ambulatorios , Adolescente , Niño , Preescolar , Estudios Transversales , Femenino , Humanos , Lactante , Recién Nacido , Italia , Mediciones Luminiscentes/métodos , Masculino , Valores de Referencia , Análisis de RegresiónRESUMEN
BACKGROUND/OBJECTIVE: Although pharmacological GH stimulation tests are still considered the gold standard for GH deficiency (GHD) diagnosis, they are burdened by poor specificity. The majority of children diagnosed as having GHD show normal GH responses when re-tested at the end of growth, thus questioning the initial diagnosis. We evaluated the concordance between IGF-I levels and GH responses to provocative tests. METHODS: We analyzed 105 GHRH plus arginine tests, 79 arginine tests, and 124 clonidine tests performed in 192 short children. IGF-I levels ≤-2SD score (SDS) were considered suggestive for high likelihood of GHD. The percentage of positive and negative results for each test was determined and compared with IGF-I levels, clinical follow-up and response to therapy. RESULTS: In children with IGF-I>-2SDS the arginine test showed a concordance rate of 6.9%, the clonidine test of 28.6%, and GHRH plus arginine test of 70%. In children with IGF-I≤-2SDS the concordance was 96.1%, 85.7%, and 46.4%, respectively. The overall concordance was 66.7% for GHRH plus arginine, 42.7% for clonidine, and 27.8% for arginine tests. CONCLUSION: Our results suggest that GHRH plus arginine test provides the best concordance with the assessment of IGF-I levels thus suggesting that the combination of the two procedures may significantly reduce the need of a second provocative test.