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Abstract

We established age- and sex-related reference ranges for serum insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) levels in 807 healthy Turkish children (428 boys, 379 girls), and constructed a model for calculation of standard deviation scores of IGF-I and IGFBP-3 according to age, sex and pubertal stage. Serum IGF-I and IGFBP-3 concentrations tended to be higher in girls compared to boys of the same ages, but the differences were statistically significant only in pubertal ages (9-14 years) for IGF-I and only in prepubertal ages for IGFBP-3 (6-8 years) (p < 0.05). Peak IGF-I concentrations were observed earlier in girls than boys (14 vs. 15 years, Tanner stage IV vs. V) starting to decline thereafter. IGFBP-3 levels peaked at age 13 and at Tanner stage IV in both sexes with a subsequent fall. Serum levels of IGF-I and IGFBP-3 increased steadily with age in the prepubertal stage followed by a rapid increase in IGF-I in the early pubertal stages. A relatively steeper increase in IGF-I but not in IGFBP-3 levels was observed at age 10-11 years in girls and at 12-13 years in boys which preceded the reported age of pubertal growth spurt. At late pubertal stages, both IGF-I and IGFBP-3 either did not change or decreased by increasing age. Interrelationships between growth factors and anthropometric measurements have been described, and the physiologic consequences of these have been discussed in detail. Differences in the pattern of IGF-I and IGFBP-3 in the present paper and those reported in other studies emphasize the importance of locally established reference ranges. Establishment of this reference data and a standard deviation score prediction model based on age, sex and puberty will enhance the diagnostic power and utility of IGF-I and IGFBP-3 in evaluating growth disorders in our population. Copyright 2006 S. Karger AG, Basel

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Insulin-like growth factors I and II. Peptide, messenger ribonucleic acid and gene structures, serum, and tissue concentrations.

W H Daughaday, P Rotwein (1989)

There is currently widespread interest in the IGFs (IGF-I and IGF-II) and their roles in the regulation of growth and differentiation of an ever increasing number of tissues are being reported. This selective review focused on the current state of our knowledge about the structure of mammalian IGFs and the multiple forms of mRNAs which arise from alternative splicing and promoter sites which arise from gene transcription. Current progress in the immunological measurement of the IGF is reviewed including different strategies for avoiding binding protein interference. The results of measurements of serum IGF-I and IGF-II in fetus and mother and at various stages of postnatal life are described. Existing knowledge of the concentration of these peptides in body fluids and tissues are considered. Last, an attempt is made to indicate circumstances in which the IGFs are exerting their actions in an autocrine/paracrine mode and when endocrine actions predominate. In the latter context it was concluded that an important role for GH action on skeletal tissues via hepatic production of IGF-I and endocrine action of IGF-I on growth cartilage is likely.

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Reference ranges for two automated chemiluminescent assays for serum insulin-like growth factor I (IGF-I) and IGF-binding protein 3 (IGFBP-3).

Martin Elmlinger, Werner Kühnel, Matthias M. Weber … (2004)

Assays for insulin-like growth factor I (IGF-I) and IGF-binding protein 3 (IGFBP-3) have become essential tools in the diagnostic work-up of disorders of the somatotropic axis in children and adults. The aim of this study was to evaluate the automated IMMULITE IGF-I and IGFBP-3 assays and to establish reference limits--central 95% intervals, median, 0.1 and other centiles as clinically relevant--as a function of age from 797 females and 787 males, from the first week of life through the ninth decade. Pubertal children were classified by sex and by sexual maturation (Tanner stage). IGF-I and IGFBP-3 levels were also assayed in 20 pediatric patients each with growth hormone deficiency (GHD) and Turner syndrome (UTS), before and during 12 months of recombinant growth hormone (rhGH) therapy, as well as in 11 adult patients with GHD and seven with acromegaly before therapy. Both the IGF-I and IGFBP-3 assays were accurate, specific and sufficiently sensitive to measure IGF-I and IGFBP-3 in serum with good linearity and recovery. In the IGF-I assay, potential interference from IGFBPs was eliminated by blocking with excess IGF-II. Circulating IGF-I and IGFBP-3 concentrations, and their ratio IGF-I/IGFBP-3, were age-dependent, showing low levels immediately after birth, a typical pubertal peak for girls and boys, and a pronounced decline after puberty, reaching a plateau in early adulthood. In adults IGF-I and IGFBP-3 levels decreased smoothly but steadily with age. Children with GHD and UTS had low circulating IGF-I and IGFBP-3 levels which increased to normal reference limits under therapy with rhGH. Adult GHD patients showed IGF-I levels below the age-related median; untreated acromegalic patients mostly had IGF-I and IGFBP-3 levels above the age-related 97.5th centile. In conclusion, the automated IMMULITE IGF-I and IGFBP-3 assays are reliable tools in the diagnosis of pathologies of the GH/IGF axis and in the follow-up of their therapies.