NORMATIVE DATA FOR INSULIN-LIKE GROWTH-FACTORS (IGFS), IGF-BINDING PROTEINS, AND GROWTH HORMONE-BINDING PROTEIN IN A HEALTHY SPANISH PEDIATRIC POPULATION - AGE-RELATED AND SEX-RELATED CHANGES

The normal values of insulin-like growth factors (IGFs) after extracti on, their binding proteins, and the high affinity GH-binding protein a re not well established in infancy or childhood. We report the relatio nship between serum IGF-I, IGF-II, their binding proteins IGFBP-1 and IGFBP-3, and GH-binding protein in 600 normal Spanish children who whe re divided into 5 groups according to Tanner stage: I, 150 males and 1 02 females; II, 40 males and 42 females; III, 45 males and 45 females; IV, 42 males and 55 females; and V, 23 males and 56 females. Serum IG F-I levels increase slowly during childhood in both sexes, exhibiting a dramatic increase during puberty and a significant decline [P < 0.00 1, by analysis of variance (ANOVA)] during adulthood. The pubertal pea k occurs approximately 2 yr earlier in girls than in boys. In contrast , serum IGF-II levels remain stable throughout childhood, showing no p ubertal peak. In boys, there is a significant decline in IGF-II levels during adulthood (P < 0.001). Serum IGFBP-3 levels show a pattern sim ilar to that of IGF-I, with a significant increase during childhood an d a significant decline during adulthood (P < 0.001, ANOVA) in both ma les and females. In contrast, serum IGFBP-1 levels decrease dramatical ly during childhood in both boys and girls (P < 0.001 and P < 0.005, r espectively, by ANOVA). A significant decline in serum GH-binding prot ein levels is observed between prepubertal and pubertal children of bo th sexes (P < 0.001). There is a close linear correlation between the sum of serum IGF-I plus IGF-II levels vs. serum IGFBP-3 (r = 0.724; P < 0.0001). In contrast, there is a nonlinear correlation between serum IGF-I vs. serum IGFBP-3 (concave curve) as well as between serum IGF- II and serum IGFBP-3 (convex curve). A negative correlation was found between serum IGF-I vs. IGFBP-1 (r = -0.51; P < 0.0001) as well as bet ween the sum of serum IGF-I plus IGF-II vs. IGFBP-1 (r = -0.47; P < 0. 0001), but not between serum IGF-II and IGFBP-1. These data emphasize that when these tests are performed in the clinic, their interpretatio n should be based upon age- and sex-specific criteria.