Normal levels of serum IGF-I: determinants and validity of current reference ranges.

Insulin like growth factor I (IGF-I) represents the key marker for the evaluation of Growth hormone (GH) status. As a large number of determinants including age, gender, genetic factors, nutrition, and disease states influence IGF-I serum levels, accurate normative data are essential to translate patient data into diagnostic meaning or even use IGF-I levels for adequate monitoring of patients with an over- or under-active GH axis. Even though reference ranges have been developed in large cohorts of healthy subjects, the dependency of these data on a given assay technology argues for assay specific normative data for IGF-I.