The routine use of these biomarkers in clinical practice faces numerous constraints: assay standardization (particularly for hepcidin) and pediatric reference ranges; variable influence of inflammation, infection and nutritional status on sTfR; access and cost—not all centers have hepcidin or RET-He available; a relative lack of large RCTs that randomize pediatric patients to biomarker-guided vs. standard care. The gene discussed is HAMP; the disease is infection.