|Iron and Total Iron Binding Capacity (TIBC)|
Uncomplicated iron deficiency: Serum transferrin (and TIBC) high, serum iron low, saturation low. Usual causes of depleted iron stores include blood loss, inadequate dietary iron. RBCs in moderately severe iron deficiency are hypochromic and microcytic. Stainable marrow iron is absent. Serum ferritin decrease is the earliest indicator of iron deficiency if inflammation is absent.
Anemia of chronic disease: Serum transferrin (and TIBC) low to normal, serum iron low, saturation low or normal. Transferrin decreases with many inflammatory diseases. With chronic disease there is a block in movement to and utilization of iron by marrow. This leads to low serum iron and decreased erythropoiesis. Examples include acute and chronic infections, malignancy and renal failure.
Sideroblastic anemia: Serum transferrin (and TIBC) normal to low, serum iron normal to high, saturation high.
Hemolytic anemias: Serum transferrin (and TIBC) normal to low, serum iron high, saturation high.
Hemochromatosis: Serum transferrin (and TIBC) slightly low, serum iron high, saturation very high.
Protein depletion: Serum transferrin (and TIBC) may be low, serum iron normal or low (if patient also is iron deficient). This may occur as a result of malnutrition, liver disease, renal disease (eg, nephrosis) or other entities.
Liver disease: Serum transferrin variable; with acute viral hepatitis, high along with serum iron and ferritin. With chronic liver disease (eg, cirrhosis), transferrin may be low. Patients who have cirrhosis and portacaval shunting have saturated TIBC/transferrin as well as high ferritin.2
Chronic dialysis for renal failure: monitor iron levels in patients undergoing dialysis. To follow treatment of iron overload with deferoxamine or with regimen of recombinant human erythropoietin and phlebotomy.3
Serum iron is decreased with insufficient dietary iron, chronic blood loss (including the hemolytic anemias paroxysmal nocturnal hemoglobinuria), inadequate absorption of iron and impaired release of iron stores as in inflammation, infection and chronic diseases. The combination of low iron, high TIBC and/or transferrin and low saturation indicates iron deficiency. Without all of these findings together, iron deficiency is unproven.2 Low ferritin supports the diagnosis of iron deficiency. Detection of iron deficiency may lead to detection of adenocarcinoma of gastrointestinal tract, a point which cannot be overemphasized. In recovery from pernicious anemia, especially just after B12 dose, iron levels are low. In fact, the drop in serum iron 1 to several days after the Schilling test flushing dose of vitamin B12 may be more useful in diagnosis than the radioactivity of the 24-hour urine collection. Serum iron is reported to drop with acute infarct of myocardium.
TIBC is increased in iron-deficiency, use of oral contraceptives, and in pregnancy.
TIBC decreased in hypoproteinemia from many causes, and in a number of inflammatory states.
Increased saturation occurs with HLA-related (classical) hemochromatosis before ferritin is greatly increased, and also with iron overload (eg, cirrhosis and portacaval shunt), in hemolytic anemias and with iron therapy. Saturation of >70% in females, >80% in males is described as prerequisite for parenchymal loading. However, sample contamination and the vagaries of fluctuation in serum iron levels can make such criteria misleading on occasion.2
The serum ferritin is a more sensitive test than the serum iron or TIBC for iron deficiency and for iron overload.2 When all these tests are used together, as is often necessary, they usually can distinguish between iron deficiency anemia and the anemia of chronic disease. The best and most reliable evaluation of total body iron stores is by bone marrow aspiration and biopsy. The best evaluation of iron deficiency in childhood (unless lead toxicity is suspected) is free erythrocyte porphyrins.
With recombinant erythropoietin therapy serum iron, transferrin saturation, and ferritin levels decline due to rapid utilization by stimulated erythropoiesis with resultant decrease in storage iron.3,5
While iron is usually considered in relation to hematopoiesis and oxygen transport functions of red cells, it is also of prime import to the lymphomyeloid systems.6