The specific objectives of this study are (1) to describe the changes in a range of markers of iron metabolism at PICU discharge, 2 months, and 6 months post-PICU; (2) to apply diagnostic algorithms for ID and AI; (3) to assess the different causes of anemia and (4) to determine a cut-off value for hepcidin (iron-marker) for identification of ID in patients with inflammation. This evidence concerns the gene HAMP and anemia (phenotype).