3. Iron overload (serum ferritin concentration ≥ 1,500 ng/mL). The serum ferritin concentration is an acute phase reactant that is increased during critical illness regardless of total body iron. Substantial levels of hyperferritinemia (serum ferritin concentration > 1,000 ng/dL) were observed in both NCT00450177 and NCT01180894 without increased risk of infection and despite both low TSAT and IDE. For these reasons, we believe that relative hyperferritinemia (serum ferritin concentration 500 - 1,500 ng/dL) is neither harmful nor indicative of bone marrow iron availability.