Anisocytosis is a medical term meaning that a patient's red blood cells are of unequal size. This is commonly found in anemia and other blood conditions. False diagnostic flagging may be triggered by an elevated WBC count, agglutinated RBCs, RBC fragments, giant platelets or platelet clumps. In addition, it is a characteristic feature of bovine blood.

Human red blood cells from a case of anisocytosis.

The red cell distribution width (RDW) is a measurement of anisocytosis[1] and is calculated as a coefficient of variation of the distribution of RBC volumes divided by the mean corpuscular volume (MCV)


Anisocytosis is identified by RDW and is classified according to the size of RBC measured by MCV. According to this, it can be divided into

Increased RDW is seen in iron deficiency anemia and decreased or normal in thalassemia major (Cooley's anemia), thalassemia intermedia

  • Anisocytosis with normal RBC size – Early iron, vit B12 or folate deficiency, dimorphic anemia, Sickle cell disease, chronic liver disease, Myelodysplastic syndrome[2]


From Ancient Greek: an- without, or negative quality, iso- equal, cyt- cell, -osis condition[3]

See also


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