Immunlite 2000

HGH concentration was determined using Immulite 2000, a commercially available kit from Siemend AG (Muenchen, Germany). A growth hormone releasing hormone + arginine stimulation rest calibrated with both IS 80/505 and IS 98/574 (GRH Growth Hormone-Recombinant 98/574-kit).
Insulin-like growth factor-1 (IGF-1) concentrations were measured using a solid-phase enzyme-labelled chemiluminescent immunometric assay on the Immunlite 2000 automated Immunoanalyzer (Siemens AG).
For measuring BDNF concentrations, a commercially available kit from R&D Systems, Inc. (Minneapolis, USA), was used. Diluted serum was used to determine the optical density of each sample well within 30 minutes at 450 nm.

Fasting blood samples were collected by a licensed phlebotomist and transported directly to the UCLA Clinical Immunology Research Laboratory (CIRL) for processing and storage at −80°C until analysis. C-reactive protein (CRP) and insulin testing was performed by the CIRL. Glucose, triglycerides, and high density lipoprotein- (HDL-) cholesterol testing was performed by the UCLA Clinical Laboratory.
Serum CRP was measured by a high-sensitivity sandwich enzyme immunoassay from Immundiagnostik. Interassay precision (expressed as percent coefficient of variation) ranged from 8.1% to 11.4% over a wide range of CRP concentrations. Plasma glucose was measured by the glucose oxidase method (measures oxygen consumption using an oxygen detecting electrode) on a Beckman Synchron LX20 automated system. Plasma insulin was measured by a sandwich immunoassay on the Siemens IMMUNLITE 2000 automated system. Serum triglycerides were measured on the Beckman Synchron LX20 automated system by a coupled enzymatic method that produces a red-colored complex. HDL-cholesterol was quantitated on the Beckman Synchron LX20 automated system using an elimination enzymatic assay from Polymedco. All tests were performed using the same lot of reagents or assay plates in order to minimize variability due to differences in reagent lots.

GH and IGF-1 were measured using SIEMENS IMMUNLITE 2000 methodology (GH calibrated against WHO NIBSC IS 98/574) [15 (link)]. Cortisol, prolactin and oestradiol were measured by immunoassay on the SIEMENS ADVIA CENTAUR. LH, FSH, TSH and free T4 were measured by chemiluminescence using SIEMENS ADVIA CENTAUR and testosterone was measured using isotope-dilution liquid chromatography–tandem mass spectrometry [15 (link)]. All assays were performed in the routine clinical biochemistry laboratories within the Leeds Teaching Hospitals NHS Trust and have been regularly validated by internal quality control (IQC) and external quality assessment (EQA) [15 (link)].