[Show Section Outline]

Iron plays a principal role in erythropoiesis, because it is necessary for proliferation and maturation of RBCs and for hemoglobin synthesis. Of the body's normal 4 g of iron (somewhat less in women), about 65 percent resides in hemoglobin and about 3 percent in myoglobin. A tiny but vital amount of iron is found in cellular enzymes, which catalyze the oxidation and reduction of iron. The remainder is stored in the liver, bone marrow, and spleen as ferritin or hemosiderin.¹⁴

Except for blood transfusions, the only way iron enters the body is orally. Normally, only about 10 percent of ingested iron is absorbed, but up to 20 percent or more can be absorbed in cases of iron-deficiency anemia. The body is never able to absorb all ingested iron, no matter how great its need for iron. In addition to dietary sources, iron from worn-out or damaged RBCs is available for reuse in erythropoiesis.¹⁵

Serum Iron, Transferrin, and Total Iron-Binding Capacity

Any iron present in the serum is in transit among the alimentary tract, bone marrow, and available iron-storage forms. Iron travels in the bloodstream bound to transferrin, a protein (-globulin) manufactured by the liver. Unbound iron is highly toxic to the body, but generally much more transferrin is available than that needed for iron transport. Usually, transferrin is only 30 to 35 percent saturated, with a normal range of 20 to 55 percent. If excess transferrin is available in relation to body iron, the percentage saturation is low. Conversely, in situations of iron excess, both serum iron and percentage saturation are high.

Measurement of serum iron is accomplished by using a specific color of reagent to quantitate iron after it is freed from transferrin. Transferrin may be measured directly through immunoelectrophoretic techniques or indirectly by exposure of the serum to sufficient excess iron such that all the transferrin present can combine with the added iron. The latter result is expressed as total iron-binding capacity (TIBC). The percentage saturation is calculated by dividing the serum iron value by the TIBC value.

Ferritin

Iron is stored in the body as ferritin or hemosiderin. Many individuals who are not anemic and who can adequately synthesize hemoglobin may still have decreased iron stores. For example, menstruating women, especially those who have borne children, usually have less storage iron. In contrast, persons with disorders of excess iron storage such as hemochromatosis or hemosiderosis have extremely high serum ferritin levels.¹⁶

Serum ferritin levels are used to measure iron-storage status and are obtained by either radioimmunoassay or enzyme-linked immunoassay. The amount of ferritin in the circulation usually is proportional to the amount of storage iron (ferritin and hemosiderin) in body tissues. Note that serum ferritin levels vary according to age and gender (Fig. 1—3).

[Section Outline]

• Serum Iron, Transferrin, and Total Iron-Binding Capacity
• Ferritin

[Show Table Outline]

Conventional Units	SI Units
Serum Iron
Newborns	350-500 mg/dL	62.7-89.5 mmol/L
Children	40-200 mg/dL	7.2-35.8 mmol/L
Adults Men	60-170 mg/dL	10.7-30.4 mmol/L
Adults Women	50-130 mg/dL	9.0-23.3 mmol/L
Adults Elderly persons	40-80 mg/dL	7.2-14.3 mmol/L
Transferrin
Newborns	60-170 mg/dL	0.6-1.7 g/L
Adults	250-450 mg/dL	2.5-4.5 g/L
% Saturation (of Transferrin)
Newborns	65% saturation	0.65
Adults	20-55% saturation	0.20-0.55
TIBC
Children	100-350 mg/dL	18-63 mmol/L
Adults	300-360 mg/dL	54-64 mmol/L
Elderly persons	200-310 mg/dL	36-56 mmol/L
Ferritin
Children	20-40 mg/dL	20-40 mg/L
Adults Men	50-200 mg/dL	50-200 mg/L
(average 100 mg/dL)	(avg 100 mg/L)
Adults Women (menstruating)	12-100 mg/dL	12-100 mg/L
(average 30 mg/dL)	(avg 30 mg/L)

[Table Outline]

• Serum Iron
• Transferrin
• % Saturation (of Transferrin)
• TIBC
• Ferritin

• Anemia of unknown etiology to determine cause and type of anemia:
  • Decreased serum iron with increased transferrin levels is seen in iron-deficiency anemia and blood loss.
  • Decreased serum iron and decreased transferrin levels may be seen in disorders involving diminished protein synthesis or defects in iron absorption (e.g., chronic diseases, infections, widespread malignancy, malabsorption syndromes, malnutrition, nephrotic syndrome). Percentage saturation of transferrin may be normal if serum iron and transferrin levels are proportionately decreased; if the problem is solely one of protein homeostasis (with normal iron stores), percentage saturation will be high.
• Support for diagnosing hemochromatosis or other disorders of iron metabolism and storage:
  • Serum iron and ferritin levels may be elevated in hemochromatosis and hemosiderosis; percentage saturation of transferrin is elevated, whereas TIBC is decreased.
  • Serum iron levels can be elevated in lead poisoning, after multiple blood transfusions, and in severe hemolytic disorders that cause release of iron from damaged RBCs.
• Monitoring hematologic responses during pregnancy, when serum iron is usually decreased, transferrin levels are increased (in the third trimester), percentage saturation is low, TIBC may be increased, and ferritin may be decreased (Note: Transferrin levels may be increased in women taking oral contraceptives, whereas ferritin levels may be decreased in women who are menstruating or who have borne children.)

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

• Blood for serum iron and TIBC should be drawn in the morning, in the fasting state, and 24 hours or more after discontinuing iron-containing medications.¹⁷

A venipuncture is performed and the sample collected in a red-topped tube. A capillary sample may be obtained in infants and children as well as in adults for whom venipuncture may not be feasible.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample (see Appendix I).

• Food, fluids, and medications withheld before the test may be resumed after the sample is obtained.
• Complications and precautions: Note and report signs and symptoms of anemia: decreases in test levels, fatigue and weakness, increased pulse, exertional dyspnea, and dizziness. If anemia is caused by blood loss, prepare to administer a transfusion of blood products. If anemia is caused by iron deficiency, administer ordered oral or parenteral (intramuscular) iron supplement and instruct client in dietary inclusion of foods high in iron content. After 4 to 7 days, check iron studies, RBC count, reticulocyte count, and hemoglobin levels to see whether iron stores have been replenished.