Anisocytosis Definition

Anisocytosis is a deficiency in iron characterized by red blood cells of unequal size. Ideally, red blood cells should be of equal size.

If there is an increased variation in the sizes of red blood cells, then it is an indicator that there is something wrong with your blood. Anisocytosis comes from the word aniso meaning unequal and cytosis meaning movement or number of cells.

Anisocytosis is not a condition alone but is caused by another medical condition, specifically anemia and/or blood-related disorders. It can also be a result of drugs used to treat cancer. Anisocytosis or the unequal distribution of red blood cells is used as a basis to diagnose blood-related disorders like anemia. (1, 2, 3, and 4)

red blood cell (RBC) distribution with noticeable uneven size and shapes

Image 1: A red blood cell distribution with noticeable uneven size and shapes.
Picture Source:

Red blood cells and the degenerative form

Image 2: Red blood cells and the degenerative form.

Types of Anisocytosis

  • Macrocytosis – the red blood cells are larger than the normal.
  • Microcytosis – the size of red blood cells are smaller than the normal.
  • Some red blood cells are larger and some are smaller than the normal size. (4, 5)

Signs and Symptoms

  • The patient gets tired easily.
  • The patient may have an episode of shortness of breath even with minimal exertion.
  • The patient complains of headache and dizziness.
  • The hands and feet are cold to touch.
  • The skin looks pale.
  • The patient complains of weakness and fatigue.
  • The patient complains of chest pain. (4, 5, and 6)

Note – The symptoms are caused by a lack of oxygen supply in vital organs and tissues of the body.

classic manifestations of patients with iron deficiency anemia

Image 3: The classic manifestations of patients with iron deficiency anemia.
Picture Source:

What are the causes of anisocytosis?

Anemia is one of the primary causes of anisocytosis. There are different types of anemia and the most common ones that are linked with anisocytosis are the following:

  1. IDA (iron deficiency anemia) – it is caused by insufficient iron in the body. A deficiency in iron can be caused by massive blood loss or not being able to eat iron-rich foods. Iron deficiency anemia is the most common form of anemia.
  2. Sickle cell anemia – It is characterized by abnormal crescent-shaped red blood cells. It is genetic in nature. If you have a family history of sickle cell disease, then you have to be extremely cautious with your health.
  3. Autoimmune haemolytic anemia – The immune system of the body destroys red blood cells as they are mistaken for a foreign object.
  4. Thalassemia – It is a genetic disorder caused by the body’s production of abnormal hemoglobin.
  5. Megaloblastic anemia – it is caused by a deficient number of red blood cells and the size is larger than the usual. Megaloblastic anemia is a result of vitamin b12 or folate deficiency.
  6. Pernicious anemia – It is caused by the body’s inability to absorb vitamin b12.
  7. Other medical conditions – aside from blood-related disorders, there are other medical conditions linked with the development of anisocytosis. These are:
    1. Chronic liver disease
    2. Myelodysplastic syndrome
    3. Thyroid-related disorders
    4. Cardiovascular-related diseases
    5. Cytotoxic chemotherapy drugs or drugs used to treat cancer (2, 4, 6, 7, and 8)


Blood Smear

A blood sample is withdrawn and a thin layer of blood is smeared on the slide, stained, and examine under a microscope. Staining is done to help in differentiating the cells. Hence, it would be easier for the doctor to see the shape and size of red blood cells. The doctor will note the following:

  • Number of red blood cells
  • Amount of hemoglobin in every red blood cell
  • Cell volume
  • Hemoglobin concentration in every red blood cell
  • Width of red blood cell (8, 9, and 10)

If there is indeed abnormalities in the size and number of red blood cells, further testing and evaluation have to be made to find out the root cause of your condition. The doctor will ask you about your past medical history and health habits such as:

  • Your diet
  • Family medical history
  • Drugs/medications you are currently taking (2, 4)

Other procedures your doctor might order are:

  • Complete blood count
  • Folate test
  • Vitamin b12 test
  • Ferritin test
  • Serum iron level (1, 3, and 5)

Treatment for Anisocytosis

The direction of treatment is dependent on what is causing anisocytosis. If it is caused by anemia, then it is treated using supplements as well as diet and lifestyle modification.

Those who have a severe type of anemia such as sickle cell, thalassemia, and the likes require more than just taking supplement and modification of lifestyle and diet.

They need to receive a blood transfusion and depending on the case, some may require a lifetime blood transfusion. For patients with myelodysplastic syndrome, the best remedy is a bone marrow transplant. (2, 5, 6, and 8)

Is anisocytosis during pregnancy a cause for concern?

Anisocytosis during pregnancy should not be a cause for concern, especially if the woman has no family history of blood-related disorder. One of the common reasons for anisocytosis during pregnancy is iron deficiency anemia, which can be easily corrected with diet and supplement.

Pregnant women are at high risk for iron deficiency anemia primarily because their body needs plenty of iron to make red blood cells for their baby. It is the reason why doctors put pregnant women in iron supplements and highly encouraged them to drink milk rich in vitamin B12 and folate.

Iron deficiency anemia during pregnancy should be addressed right away as it could have a negative effect both to the mother and the baby. It might lead to:

  • Pre-term labor and other pregnancy complications
  • Insufficient supply of oxygen to the growing fetus
  • Weakness and fatigue to the mother
  • The possibility of birth-related defects, especially in the brain and spinal cord (3, 6, 9, and 10)

How to prevent anisocytosis?

  • Watch your diet, especially if you are pregnant. You should increase your intake of nutritious foods, especially foods rich in iron, vitamin b12, and folate.
  • Lead a healthy life.
  • If you are not used to eating iron-rich foods, then your best option is to take supplements such as iron supplements and vitamin B12. (2, 4, and 7)



It is a medical term for abnormally shaped red blood cells. It is not a disease itself but an indicator of an underlying medical condition like anemia, alcoholism, liver disease, and blood-related disorders. Symptoms include the following:

  • Abnormally shaped red blood cells (greater than 10%)
  • Fatigue
  • Weakness
  • Pale skin
  • Shortness of breath

What is the difference between anisocytosis and poikilocytosis?

The primary difference between anisocytosis and poikilocytosis is that the former is characterized by red blood cells of different sizes while the latter is red blood cells of varying shapes.


  10. Diagnostic Hematology By Norman Beck

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