Establishment of Reference Values for Insulin-like Growth Factor 1 (IGF1) in the General Population

Overview

Various assays can be used for IGF-I measurement in French laboratories. Unfortunately, each assay gives a very different result for the same sample. As IGF-I also varies with age, it is necessary to establish a broad population reference values of IGF1 concentration for each of the IGF1 assays used in clinical practice, taking into account individual variation factors such as age, nutritional status and possible treatments. The objective of this study is to establish normative data based on a large random selection from the general population, including representation from all age groups (around 100 subjects for each decade age range). This will be performed for all the available assay kits. Subjects with medical conditions and medications that may affect the outcome will be excluded. Normative data will include the range (2.5 to 97.5 percentiles) in mass units and results will be reported as mass units but also as SD scores in order to be able, in a given patient, to compare its IGF-I concentration along time, even if using different assays.

Healthy subjects will be recruited in 30 centers all around France. A total of 1000 healthy subjects are necessary. Each subject will have a clinical examination with measurement of height and weight. Personal medical history will be recorded and gonadal status evaluated. Biological standard workup will be performed and 80 ml of blood will be sampled and serum will be aliquoted, frozen and stored at -80°C. IGF-I level will be measured with all the assay methods available (sera kept in bank will be used in the future when new methods will be available) For each assay method and each age group (Four 3-years groups between 18 and 30 years and six decade age groups between 30 and 89 years) IGF-I will be measured. Results will be expressed as mean, median, standard deviation, 2.5th and 97.5th percentiles, in mass units. Modelisation according to age and other factors will be performed in order to allow the reporting of IGF-I results for a given individual expression of IGF-I as Z-score.