Microcyte

Microcyte
Peripheral blood smear, Wright-Giemsa stain, 500x

Description:

A red cell that is smaller than a normal red cell. On a given blood smear, the size of a normal red cell is approximately that of the nucleus of a very small lymphocyte. Depending on the percentage of microcytes present, the MCV will be low and reflect the degree of microcytosis. If the RDW is increased, due to the presence of anisocytosis, the MCV may not reflect the degree of microcytosis. Most microcytes are hypochromic.

Pathobiology:

The hypochromia is due to decreased hemoglobin synthesis but the mechanism for the decrease in size of the red cell is less clear.

Differential diagnosis:

  • Iron deficiency- in addition to hypochromic microcytes, hypochromic elliptocytes (pencil cells) are frequently seen. In severe cases poikilocytosis may be marked.
  • Anemia of chronic disease (inflammation)
  • Anemia of neoplasia
  • β-Thalassemia trait
  • β-Thalassemia intermedia and major
  • αβ-Thalassemia trait and disease
  • α-Thalassemia trait
  • Hemoglobin C trait and disease (target cells also seen)
  • Hemoglobin E trait and disease
  • Hemoglobin H disease
  • Hemoglobin Lapore trait 
  • Unstable hemoglobinopathies
  • Lead poisoning (basophilic stippling also seen)
  • Myelodysplastic syndromes with dyserythropoiesis- macrocytes are more characteristic in the acquired forms, and despite the presence of a variable degree of anisopoikilocytosis, the MCV is usually elevated. 
    • Drugs, e.g. isoniazid (INH), chloramphemical,
    • Toxins, e.g. lead (basophilic stippling usually prominent)
  • Hereditary sideroblastic anemia (usually sex-linked)
  • Other hereditary disorders of iron and heme metabolism
    • Atransferrinemia (hemochromatosis-associated)
    • acerulopalsminemia (hemochromatosis-associated)
    • ferrochelatse (heme synthetase) deficiency
    • hemeoxygenase deficiency
    • divalent metal transporter 1 (DMT 1) deficiency

 

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Charles  E.  Hess,  M.D.,FACP    [more information]
Professor of Internal Medicine
Department: Medicine
Division: Hematology/Oncology