Iron Deficiency Anemia and Anemia of Chronic Disease

Iron Deficiency Anemia

Diagnostic Features

Smear Features and Hemoglobin Indices

• Normal Red Cell:
  • Normocytic with a normal MCV (Mean Corpuscular Volume).
  • Zone of central pallor is one-third the size of the cell.
• Microcytic Hypochromic Cell:
  • Smaller cell with MCV < 80.
  • Larger zone of central pallor.
• Poikilocytosis: Abnormally shaped red cells.
• Anisocytosis: Red cells of abnormal size.

Differential Diagnoses

• Thalassemia: Low MCV with target cells in the smear.
• Spherocytosis:
  • Normal-sized red cells initially, shrink after spleen passages.
  • Not hypochromic.

Indices

• MCHC (Mean Corpuscular Hemoglobin Concentration):
  • Decreased in iron deficiency anemia and thalassemia.
  • Increased in spherocytosis (membrane defect).

Key Diagnostic Findings

• Low Serum Iron Level: Indicates iron deficiency.
• High Total Iron Binding Capacity (TIBC):
  • Indicates many empty binding sites on transferrin.
  • Increased transferrin synthesis.
• Low Iron Saturation: Iron to TIBC ratio less than 10%.
• Low Ferritin: Reflects low total body iron stores.

Bone Marrow

• Iron Stores: Depleted in iron deficiency anemia.

Iron Binding Capacity

• High TIBC: Many available seats on transferrin (empty trolley analogy).
• Low TIBC in Iron Overload: Full seats, decreasing capacity.
• Iron Saturation: Ratio of iron to TIBC; low in iron deficiency anemia.

Common Etiologies

• Blood Loss: Chronic GI blood loss is common; also consider uterine fibroids and nutritional deficiencies.
• Malabsorption Syndromes: Often accompanied by diarrhea and low iron (e.g., celiac disease).
• Menstrual Blood Loss: Common, straightforward iron deficiency.

Anemia of Chronic Disease

Key Features

• Inflammatory Cytokines: Especially IL-6, leading to increased hepcidin.
• Hepcidin: Degrades ferroportin, trapping iron in cells.

Lab Findings

• Mild Anemia: Slightly reduced MCV, no reticulocytosis.
• Low Transferrin: Decreased TIBC due to reduced transferrin levels (negative acute phase reactant).
• Iron Saturation: Low normal range.
• Ferritin: Normal or elevated, an acute phase reactant.
• Bone Marrow: Shows normal iron stores, Hemosiderin stains positively.

Comparisons to Iron Deficiency Anemia

• TIBC: High in iron deficiency, low in anemia of chronic disease.
• Iron Saturation: Very low in iron deficiency, low normal in chronic disease.
• Ferritin: Low in iron deficiency, normal/elevated in chronic disease.
• Bone Marrow: Decreased iron stores in iron deficiency, normal iron stores in chronic disease.

Classic Question Scenarios

• Presentation: Anemic patient with inflammatory conditions, low MCV, low serum iron, distinguishing by TIBC and iron saturation.
• Erythropoietin Production: Inhibited by inflammatory cytokines, not elevated.

Conclusion

• Significant differences in diagnostic features, lab findings, and underlying causes between iron deficiency anemia and anemia of chronic disease.
• Understanding and recognizing these differences are crucial for accurate diagnosis and treatment.

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