2.9. Laboratory Analyses 
BLOOD
Determination of plasma IGF1 and IGFBP3 concentrations was performed at the University of Colorado, Boulder using an automated immune diagnostic system (IDS-iSYS Multi-Discipline Automated System; Immunodiagnosticsystems (IDS), East Boldon, UK). Blood samples collected at baseline and endline were analysed for IGF1 and IGFBP3 concentrations using IDS-iSYS IGF1 and IGFBP3 assays, with the IDS-iSYS Multi-Discipline Automated System (Immunodiagnostic Systems Holdings PLC, Boldon, UK). The LOD levels for IGF1 and IGFBP3 assays were 10 ng/mL and 80 ng/mL, respectively. The intra and inter assay CV% for the IGF1 assay were 3.4 and 6%, and for the IGFBP-3 assay were 2.5% and 5.4%, respectively. The IDS-iSYS was calibrated against a reference pediatric population and requires ~100 µL of plasma for both analytes. Plasma zinc was analyzed by inductively coupled plasma optical emission spectrophotometry (ICP-OES Agilent 5100 SVDV, Santa Clara, CA, USA) at the Children’s Hospital of Oakland Research Institute (CHORI, Oakland, CA, USA).