Assessment of iron status.

OBJECTIVE: To review the clinical assessment of iron deficiency and excess.
CONCLUSIONS: Two key iron-related proteins in the human body are ferritin which is the iron storage protein, and the transferrin receptor, which controls the entry of iron-bearing transferrin to cells. Intact ferritin and truncated transferrin-receptor molecules are present in serum in direct quantitative proportion to their total tissue content. Ferritin and transferrin-receptor production are precisely and reciprocally regulated at a posttranscriptional level. This is achieved by an iron-responsive element-binding protein that interacts with iron-responsive elements in the mRNA of each, but with contrary effects. Increases in serum ferritin reflect increased storage iron and increases in serum transferrin receptor reflect cellular iron deficits. The combined use of these two measurements allows accurate definition of the entire range of body iron status. This is valid even in situations where assessment of iron status has been notoriously problematic, including periods of rapid growth, in pregnancy, in conditions associated with inflammation, and in trained athletes.