Ids isys assay

Arginine and glucagon tests were the only GH stimulation tests used in our institution during the study period. Protocols for the arginine and glucagon stimulation tests used in our institution are available at https://mft.nhs.uk/app/uploads/2022/03/Paediatric-DFT-Protocols-V7_Feb-2022.pdf (accessed 22nd August 2022). Sex steroid priming is given in our unit for pre-pubertal girls >8 years or boys >9 years undergoing stimulation tests. Ethinylestradiol 10-20 micrograms is given once daily for 3 days prior to the test for both boys and girls. A normal test result in our institution is indicated by a peak GH level ≥ 7 μg/L. GH, IGF-I and IGFBP-3 were measured on the IDS iSYS assay (Immunodiagnostic systems, Tyne and Wear, UK). The GH assay used is standardized to the recombinant GH calibration standard World Health Organization 98/574 and complies with recommendations on assay standardization (19 (link)).

The available PK/PD model was based on serum concentrations of IGF-I analyzed at analytical laboratory Laboratorium für Klinische Forschung GmbH, Schwentinental, Germany using commercially available assay kits (Immuno Diagnostic Systems immunoassay [IDS-iSYS assay]). Normal reference ranges for the calculation of SDS were based on the publication by Bidlingmaier et al (30 (link)). It was not the scope of this analysis to assess the impact of assay variability on IGF-I calculation.