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Chapter 162 Resources for the Hematologist e5

Ferritin
Summary points • Ferritin concentration reflects body iron stores; decreased in iron deficiency, increased in iron overload
• Useful in distinguishing between iron deficiency anemia and anemia of chronic disease, thalassemia minor
• Assessment of iron deficiency may be confounded by infection, inflammation, malignancy, and liver disease, all of
which raise ferritin concentration
• More sensitive and reliable than serum iron, transferrin (total iron-binding capacity), and transferrin saturation for
detecting iron deficiency
• Is an acute-phase reactant
Methodology Immunoassay
Specimen requirements Lithium heparin or plain tube
Indications Assess suspected iron deficiency or iron overload
Reference range Table 162.9
Interpretation • Levels are age and gender dependent. Levels in adult females are generally lower than in adult males, but following
menopause progressively approach those of males
• Levels elevated with iron overload, Gaucher disease, acute hepatitis, malignancies, hemophagocytic lymphohistiocytosis,
other highly inflammatory states
Related tests Iron, transferrin (total iron-binding capacity), transferrin saturation, soluble transferrin receptor
Interfering substances Antianimal antigen antibodies

Soluble Transferrin Receptor

Summary points • Transferrin receptor derived mainly from erythroid marrow cells
• Reflects iron status independent of concurrent inflammation
Methodology Immunoassay
Specimen requirements Lithium heparin or plain tube
Indications Assess for iron deficiency, especially in setting of inflammation
Reference range Table 162.10
Interpretation • Levels decreased with erythroid hypoplasia states, increased with increased iron demand (erythroid hyperplasia
[hemolysis, recent blood loss, thalassemia], iron deficiency)
• Unaffected by inflammation or liver disease
• African Americans and individuals at high altitude may have slightly higher values
Related tests Iron, transferrin (total iron-binding capacity), transferrin saturation, ferritin
Interfering substances Lipemia

Total Iron-Binding Capacity, Transferrin Saturation
Summary points • Transferrin—the major iron transporter protein in plasma
• TIBC—often measured as transferrin concentration, especially in pediatrics, because of smaller specimen volume
required for children
• One molecule of transferrin can bind two molecules of iron
• TIBC and transferrin concentration—typically elevated in iron deficiency due to increased transferrin gene expression
• Transferrin saturation—calculated as serum iron concentration divided by the iron-binding capacity; low in iron
deficiency, elevated in iron overload
Methodology Immunoassay and calculation
Specimen requirements Lithium heparin or plain tube
Indications Assess suspected iron deficiency, iron overload, and acute iron poisoning (transferrin saturation elevated in the latter)
Reference range Table 162.11
Interpretation • Pregnancy and oral contraceptives increase transferrin concentration, leading to low transferrin saturation
• Acute-phase response can decrease transferrin and TIBC
• Spuriously high TIBC can occur with acute hepatitis and after iron dextran injection
Related tests Iron, ferritin, soluble transferrin receptor
Interfering substances Lipemia
TIBC, Total iron-binding capacity.

Iron

Summary points • Reflects recent iron ingestion and absorption
• Undergoes circadian variation
• Less reliable than ferritin for assessing iron deficiency
Methodology Spectrophotometry
Specimen requirements Lithium heparin or plain tube
Indications Assess suspected iron deficiency, iron overload, acute iron poisoning, iron absorption (iron challenge test)
Reference range Table 162.12
Interpretation • Acute-phase response, malignancy, and ascorbate deficiency can decrease iron concentration, whereas liver disease,
ineffective erythropoiesis, and aplastic and sideroblastic anemias can increase it
• For oral iron challenge testing, an increase of at least 100 µg/dL 1−4 h after ingestion of 65 mg elemental iron is
thought to indicate adequate absorption
Related tests Ferritin, transferrin (total iron-binding capacity), transferrin saturation, soluble transferrin receptor
Reference Cook JD: Diagnosis and management of iron-deficiency anaemia. Best Pract Res Clin Haematol 18:319, 2005.