Quality assurance in the analysis of growth hormone and insulin-like growth factor I in disorders of the somatotropic axis

Background: Reliable laboratory analysis is fundamental to diagnostics, therapy, and follow-up of growth disturbance and secretory dysfunction of growth hormone (GH) and insulin-like growth factor I (IGF-I). Currently available commercial assays have their limitations, as they show large variations in hormone concentrations measured. Methods: The recommendations of an expert workshop with practicing endocrinologists from the fields of pediatrics and internal medicine and with laboratory physicians, with reference to the outcome of the interdisciplinary consensus conference in Keswick (Virginia, USA) in 2009, were used. Results: Among the quality criteria stipulated by the workshop participants are the use of uniform reference standards, documentation of analytical conditions (such as calibrators, binding epitopes, cross-reactivity, and methods for removal from the binding protein), batch-to-batch consistency, and low inter-assay variability. The participants recommended developing assay-specific thresholds and reference intervals based on large and well-defined reference populations. It is furthermore recommended to delineate the assay quality, particularly with reference to clinically important cutoffs. Conclusions: The manufacturers of diagnostic assays should be obliged to regularly monitor and report the implementation of quality criteria. Only assays that are evaluated according to uniform quality standards and that are employed clinically permit informed diagnostic and therapy of patients with GH secretory dysfunction, preventing avoidable burden on both patients and paying authorities.