What is Anisocytosis?

Definition : It is a medical term for abnormally sized red blood cells. In a healthy condition, the red blood cells should be uniformed in size. In the case of anisocytosis, the red blood cells are unequal in size.

The number, shape, and variation in sizes of blood components such as red blood cells are helpful in diagnosing blood-related disorders such as anemia.

Anisocytosis itself isn’t dangerous but it is an indicator of a serious underlying medical condition, specifically problems in the red blood cells such as a possibility of sickle cell anemia. (1, 2, 3)

Unequal sized red blood cells (anisocytosis) can significantly affect the normal functions of the body image photo picture

Picture 1: Unequal sized red blood cells (anisocytosis) can significantly affect the normal functions of the body.
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Anisocytosis Symptoms

  • Macrocytosis (red blood cells are larger than the normal size)
  • Microcytosis ( the red blood cells are smaller than the normal size)
  • Some red blood cells are small while others are large.
  • A feeling of weakness and fatigue
  • The skin is cold and pale particularly the lips, fingers, and nails.
  • Trouble breathing such as shortness of breath
  • Rapid heart rate as a way for the body to cope for insufficient supply of red blood cells. (2, 4, 5, 6)

The degenerative forms of red blood cells image photo picture photo

Picture 2: The degenerative forms of red blood cells (abnormal shapes and unequal size.)
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A visual presentation on how an anisocytosis looks like image picture photo

Picture 3: A visual presentation on how an anisocytosis looks like.
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Anisocytosis Causes


The primary cause of anisocytosis is anemia. The red blood cells do not have sufficient oxygen, which deprive the tissues of oxygen content. There are various types of anemia such as:

  • IDA (Iron deficiency anemia) – The body’s iron level is insufficient secondary to dietary deficiency or massive blood loss. Iron deficiency anemia is the cause of microcytic anisocytosis.
  • SCA (sickle cell anemia) – It is caused by an abnormal crescent shape red blood cells.
  • Autoimmune hemolytic anemia – The body’s immune system attacks the red blood cells.
  • Thalassemia – The body produces abnormal haemoglobin leading to microcytic anisocytosis.
  • Pernicious anemia – It is a type of autoimmune disorder in which the body is unable to absorb vitamin B12.
  • Megaloblastic anemia – A decreased in red blood cells and the size is larger than the normal. (1, 2, 4, 5)

Vitamin Deficiency

Some essential vitamins play a vital role in the production of new red blood cells. These vitamins include vitamin A and vitamin B12. Without these vitamins, the body can’t produce adequate amount of red blood cells causing abnormally shaped and unequal sized red blood cells. (2, 3, 6)

Blood Transfusion

Anisocytosis can be caused by blood transfusion. It is most likely to happen if the receiver and donor of blood has an incompatible size of red blood cells. (7, 8)

Myelodysplastic Syndrome

It is a type of cancer in the blood wherein new blood cells in the bone marrow do not mature and fail to transition to healthy cells. (6, 7)

Other possible causes

Other health conditions linked with anisocytosis are thyroid disorders (hyperthyroidism/hypothyroidism), chronic liver disease, cardiovascular disease, and cancer.

There are certain drugs that can increase the possibility of anisocytosis such as cytotoxic chemotherapy drugs (drugs used to treat cancer). (5, 6, 7)

The significance of having a uniformly sized red blood cells

For the red blood cells to carry out their task smoothly (transport oxygen to different parts of the body), they should be equal in size and shape. If there is discrepancy in sizes, the RBCs ability to transport oxygen will be affected significantly.

Red blood cells are round and flat. If more than 10% of RBCs are abnormally shaped, the person has poikilocytosis. (7, 8)

How to diagnose Anisocytosis?

Various blood tests and diagnostic procedures are conducted to accurately diagnose anisocytosis. Anisocytosis blood test is in the form of a blood smear.

  • Blood smear – a thin layer of the patient’s blood is placed on the slide and check under the microscope for the doctor to see the size and shape of the red blood cells. If the result came in positive, the doctor will order other tests to find out the root cause of anisocytosis.
  • Blood test – The doctor specifically looks for red blood cell distribution width to check the width of the RBCs and mean cell volume to detect the actual volume/number of red blood cells.

    Anisocytosis is categorized as +1 if the irregularly sized RBCs are few. Anisocytosis +2 is when there is a huge number of irregularly sized red blood cells.

  • Depending on the overall condition of the patient, the doctor might order additional test such as vitamin B12 test, serum iron level, and ferritin test. (7, 8, 9, 10)

Diet modification is one of the natural remedies for anisocytosis image picture photo

Picture 4: Diet modification is one of the natural remedies for anisocytosis.
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Iron supplement can help in the treatment and management of patients with anisocytosis secondary to iron deficiency anemia image photo picture

Picture 5: Iron supplement can help in the treatment and management of patients with anisocytosis secondary to iron deficiency anemia.
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Patients with anisocytosis secondary to myelodysplastic syndrome should receive blood transfusion image photo picture

Picture 6: Patients with anisocytosis secondary to myelodysplastic syndrome should receive blood transfusion.
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Anisocytosis Treatment

The treatment for anisocytosis depends on the overall condition of the patient. The doctor will determine the root cause of the problem and will start and focus the treatment from there. If it is caused by anemia, the doctor will modify your diet and will prescribe supplements when deemed necessary such as iron, folate, and vitamin B12 supplement.

Diet and lifestyle modification can help improve the condition of the patient. The patient is highly encouraged to increase the intake of iron-rich foods such as meat, fish, dark and leafy vegetables, beans, nuts, eggs, and dried fruits.

For severe forms of anemia such as thalassemia and sickle cell disease, the condition cannot be corrected by diet and supplements only. The patient will require blood transfusion. For patient with myelodysplastic syndrome, a bone marrow transplant is needed. (2, 5, 9, 10)

Anisocytosis in Pregnancy

Pregnant women are usually deficient in iron because the stored iron in their blood is used by the growing baby inside the womb. This increases the possibility of anisocytosis. Hence, pregnant women are highly encouraged to increase their iron intake.

They are also given iron and folate supplement to supplement the body’s demand for iron and folate. During the routine prenatal visit, the doctor will check the iron level to find out if you have anisocytosis. An abnormal red blood cells during pregnancy shouldn’t be taken lightly. It can possess danger to the growing fetus.

If not treated right away could deprive the growing fetus of oxygen. As your tummy grows, you feel weak and tired. You will most likely experience preterm labor, birth defects, and other pregnancy complications. (1, 3, 5, 6)


The prognosis for anisocytosis primarily depends on the general health condition of the patient, the underlying cause, and the treatment and management of the patient’s condition. The prognosis is poor if anisocytosis is left untreated.

If anisocytosis is genetic in origin such as in the case of sickle cell anemia, the patient requires a life-long treatment. The patient needs blood transfusion on a regular basis. This could be financially constraining.

The ability of the family to sustain blood transfusion can affect the overall prognosis of the patient. (2, 7, 9, 10)



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