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Red Cell Distribution Width

 
 
 
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On this page:Anisocytosis
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Overview

  • Red cell distribution width (RDW) is the amount of variation in red blood cell size. Cells may be relatively uniform in size and have a low RDW, or have a wide range of sizes and have a high RDW.

      • Normal Range

      • 11 - 15%

Anisocytosis

  • Elevated red cell distribution width (RDW) indicates that red blood cells are at a large range of sizes. This phenomenon is known as anisocytosis.
  • In iron deficiency and megaloblastic anaemia, the RDW may elevate before the MCV becomes abnormal, and as such the RDW can be an early marker.

    • Causes of Anisocytosis

    • Predominantly Microcytic

    • Iron deficiency anaemia
    • Sideroblastic anaemia

    • Predominantly Normocytic

    • Early iron deficiency anaemia
    • Early megaloblastic anaemia
    • Red cell fragmentation
    • Immune haemolysis
    • Sickle cell anaemia
    • Sideroblastic anaemia
    • Blood transfusion

    • Predominantly Macrocytic

    • Megaloblastic anaemia (B12 / folate deficiency, drugs)
    • Myelodysplastic syndrome
    • Chronic liver disease
 
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