IGF-1 and IGF-1 SDS – fit for purpose?

Dear Editor, Three recent publications (1, 2, 3) have reported that the differences in IGF-1 normative data significantly impact the classification of patients with growth hormone (GH) excess and deficiency disorders in such a way that clinical performance is severely flawed. This concerns not only pediatric but also adult patients. With this letter, we aim to address additional issues, not previously addressed, which add to the complexity of the interpretation of IGF-1 results. Specifically, the relation between analytical performance of IGF-1 assays and acceptable clinical performance is discussed. Given the strong dependency of serum IGF-1 on age and gender, calculation of the IGF-1 standard deviation score (s.d.-score or SDS) is preferred as an indirect measure of the GH secretory status. However, in a consensus statement on standardization of IGF-1 assays (4), no recommendation on preferred SDS calculation is given. SDS is widely used in children for anthropometric measures, such as length, height, weight, body mass index and head circumference. However, these measures can be measured accurate and precise without variation in time, in contrast to IGF-1 measurements, which show considerable methodological and biological variability.