Anisocytosis is a medical term meaning red blood cells are of unequal size. 

This is commonly found in anemia and other blood conditions. 

The red cell distribution width (RDW) is a measurement of anisocytosis 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. 

Anisocytosis with microcytosis – Iron deficiency, sickle cell anemia

Anisocytosis with macrocytosis – Folate or vitamin B12 deficiency, autoimmune hemolytic anemia, cytotoxic chemotherapy, chronic liver disease, myelodysplastic syndrome

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

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