Iron deficiency can cause a anemia (resulting from defective RBC production). It is important to consider absolute versus functional iron deficiency. Absolute iron deficiency is the absence of storage iron for red blood cell (RBC) production. Functional iron deficiency occurs when there is a lack of available iron to support ongoing erythropoiesis, e.g. during infection or inflammation. The transferrin saturation (TSAT) and serum ferritin are used to assess deficiency. It is important to note that iron serum ferritin is an acute phase reactant and may become elevated in the presence of inflammation.
Kidney Disease: Improving Global Outcomes (KDIGO) Anemia Work Group. KDIGO Clinical Practice Guideline for Anemia in Chronic Kidney Disease. Kidney Inter., Suppl. 2012; 2: 279–335.