Purpose: Insulin-like growth factor I (IGF-I) represents an essential tool in the diagnostic work-up and in the monitoring of treatment efficacy for somatotrophic axis disorders both in children and adults. A large number of factors including, but not limited to, age, sex and weight as well as analytical variables influence IGF-I serum levels; therefore, reliable normative data are essential for a correct interpretation of results. The aim of the present study was to establish reference range values for serum IGF-I, in a large population of healthy adults from Buenos Aires city.
Methods: The study included serum samples from 1044 healthy subjects aged 21-87 years (423 females and 621 males) divided into groups by sex at 5-year intervals from 21 to >75 years. Serum IGF-I concentrations were determined by a fully automated two-site, solid-phase, enzyme-labeled chemiluminescent immunometric assay (Immulite 2000, Siemens Healthcare Diagnostics). IGF-BP interferences are circumvented by blocking IGF-BP binding sites with excess IGF-II in the on-board predilution step.
Results: Results show the age dependence of circulating IGF-I levels, with a smooth and steady decrease in levels with age. No sex differences were found in subjects >26 years; however, in the group aged 21-25 years, IGF-I levels were significantly higher in females. In conclusion, this study provides age- and gender-adjusted normal reference ranges for IGF-I levels obtained with an automated immunometric chemiluminescent assay Immulite 2000 in healthy adult subjects.