Reference levels of insulin-like growth factor I in the serum of healthy adults:: Comparison of four immunoassays

The measurement of insulinlike growth factorI (IGFI) has become an essential tool for diagnosing growth hormone deficiency and acromegaly, as well as for monitoring the efficacy of treatment in these disorders. The latter aspect gains significance in the light of epidemiological studies which indicate a relationship between IGFI levels and the incidence of certain malignancies. We aimed to evaluate the performance of widely implemented IGFI assays by testing four representative, commercially available immunoassays. Thus, four parallel determinations of the IGFI levels of 427 healthy blood donors aged between 18 and 79 years were conducted. Apart from divergent performance criteria, the assays also differed systematically. These differences were, however, linear and of lower magnitude among the lower ranges. We conclude that despite the wide variance among commercially available IGFI assays, which principally involve assayspecific normative data, each of the implemented assays was robust and thus an appropriate tool in the diagnostic workup of growth hormone deficiency in adult life, when IGFI levels are low.