Iron
None of the routinely available tests reflects iron intake; rather, they assess
body stores. Iron is not absorbed efficiently. Iron absorption is dependent on
dietary factors such as food source and the ascorbic acid content of the meal.
Hemoglobin
About 60-65% of the total body iron is in hemoglobin. Because the iron pool
is associated with hemoglobin, persons with a larger blood volume (and thus more
hemoglobin) have larger stores of iron. Males have more hemoglobin than
females.
Serum iron and iron-binding capacity
Serum iron is largely bound to the beta-globulin transferrin. There are
usually 4-6 milligrams (mg) of transferrin-bound iron in plasma with a
capacity to bind 25-30 mg. Iron is passed from the reticuloendothelial
cells to the plasma where 50% is turned over in one hour. Serum iron
measurements are unstable and vary greatly within a person and throughout the
day. Normal adult levels of serum iron range from 65-200 micrograms per
deciliter (mcg/dL). Low iron levels that do not reflect low body stores can
result from blood loss, infections, chronic illness, and malignancies. High
serum iron levels are seen in cases of megaloblastic anemia, when inflow
into the plasma is increased, and in cases of aplastic anemia, when outflow
from the plasma is decreased.
Transferrin levels are normally 350-380 mg/dL, and increase with iron deficiency
and pregnancy. Levels are decreased with chronic disease, protein deficiency,
or hepatic disease.
Interpretation of iron and transferrin are based on both values and the percent
saturation. Low serum iron and low iron-binding capacity are the best
indicators of anemia of chronic inflammation.
Ferritin
Ferritin is the major storage form of iron in the liver, spleen, and bone
marrow. Serum ferritin levels are thought to reflect body stores. Normal
values range from 15-400 nanograms (ng) per milliliter in males and 10-200
ng/ml in females. Lower values are indicative of iron deficiency with anemia.
Serum ferritin levels between 15 and 45 ng/ml may indicate a deficiency in
patients with chronic inflammation. High levels are seen with
hemochromatosis and transfusions. Serum ferritin is the best screening test
because levels fall only with decreased iron stores.
Free Erythrocyte Protoporphyrin (FEP)
Protoporphyrins cannot be utilized for the synthesis of heme during iron
deficiency; thus they will be found in higher levels when a patient is iron-
deficient. However, FEP levels rise with other disorders of heme synthesis and
so are not specific for iron deficiency anemia.
