Quantitative measurement of IGF-I and its use in diagnosing and monitoring treatment of disorders of growth hormone secretion.

Quantitative measurements of serum IGF-I concentrations are extremely useful in the diagnosis of growth hormone deficiency in children and young adults and in the diagnosis of acromegaly. Similarly, IGF-I measurements have been of great use to clinical investigators who are monitoring the effect of either growth hormone or IGF-I in various disorders. Several guidelines have proven very useful for assaying IGF-I and defining high-quality assays. Since IGF-I circulates associated with IGF binding proteins it is essential that a high-quality assay remove binding protein interference. Similarly, it is essential that the antibodies that are utilized in the assay have both high specificity and high affinity for IGF-I. Assay reproducibility is effected by such factors as quality of sample collection, utilization of proper internal and external standards and published validation using not only normal samples but samples from a variety of pathophysiologic conditions. Interlaboratory variability often is due to differences in one of more of these characteristics. When assessing the validity of abnormal assay results it is important to be able to compare the value to a normative dataset that has been developed on a large number of subjects. Recently a normative dataset was published on 2,812 subjects and this provides an important reference standard by which other assays should be judged. Careful attention to these characteristics is likely to result in valid and useful IGF-I assay results.