The measurement and interpretation of serum ferritin.

Determination of serum ferritin is an important means of assessing body iron stores. Trace amounts of ferritin normally present in serum are detectable by sensitive radioimmunoassay techniques or an enzyme immunoassay procedure. Ferritin normally accounts for no more than a very small fraction of the total iron in serum, but generally maintains a stable concentration that is proportional to the much larger pool of storage iron in tissues. The serum ferritin assay, in contrast to other measurements of iron status such as hemoglobin, serum iron and iron-binding capacity, can distinguish differences in iron stores within the physiological range. In iron deficiency anemia, the concentration is below 10 ng per ml. Increased concentrations (above 200 ng per ml) are found in conditions with increased iron stores. The information it provides is similar to that obtained from bone-marrow aspirates stained for iron. In contrast to the percent transferrin-saturation and concentration of erythrocyte protoporphyrin, ferritin concentrations become abnormal before exhaustion of mobilizable iron stores and before the onset of anemia. Serum ferritin also provides a practical means of assessing new programs of iron supplementation, since it reflects various degrees of iron deficiency and overload.