Anisocytosis

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Anisocytosis is the differing or variation in the size of some of the blood cells. It is a term usually applied to red blood cells, although is sometimes used to describe platelets too. Of particular interest to us in relation to AIHA/IMHA are the red cells – anisocytosis is commonly seen in anemia. These variations in size may be because the red blood cells have been released too early (not mature enough) or they could be damaged/faulty. For example, reticulocytes (baby red blood cells) are larger because of the RNA inclusion & on a blood smear appear much larger than a mature red blood cell.

Causes of anisocytosis include iron deficiency anemia, other anemias, AIHA/IMHA, FLV in cats, onion or garlic poisoning, cancer of the bone marrow, sickle cell anemia, liver disease & some drugs.

Anisocytosis with microcytosis (small size RBCs) – Iron deficiency, sickle cell anemia
Anisocytosis with macrocytosis (large size RBCs) – Folate or vitamin B12 deficiency, autoimmune hemolytic anemia, cytotoxic chemotherapy, chronic liver disease, myelodysplastic syndrome
Anisocytosis with normocytosis (normal RBC size) – Early iron, vitamin B12 or folate deficiency, dimorphic anemia (microcytic hypochromic and normocytic macrocytic cells), myelodysplastic syndrome, sickle cell disease, chronic liver disease

Increased RDW is seen in iron deficiency anemia, myelodysplastic syndromes, thalassemia .

False readings can be caused by a high WBC count, agglutination (clumping of RBCs), RBC remnants, giant platelets or platelet clumping.