The assessment of iron deficiency anemia in infants is a clinical challenge because of the high requirements for iron to support expansion of the blood volume during rapid growth and development. Infants are endowed with only adequate storage iron to support this iron requirement for the first 4 to 6 months of life and premature infants even less than that. Hemoglobin is a measure of anemia but is not specific to iron deficiency, which requires the additional measurement of ferritin, soluble transferrin receptor, and protoporphyrin levels to assess iron nutrition. Premature infants that receive transfusion or erythropoietin therapy are special diagnostic challenge. An accurate classification of iron status requires multiple biomarkers of iron storage and transport adequacy and in the absence of standardized assay material for several tests, becomes quite problematic.