Anisocytosis in Anemic and Nonanemic People: What Happens?
Variation in red blood cell size is an indicator of disease
Medically reviewed by Steffini Stalos, DO
Anisocytosis is a condition in which the sizes of a person’s red blood cells are more variable than usual. A complete blood count (CBC) is a test that provides information about the number, color, and size of each type of blood cell.
Any deviation from standard measurements can indicate disease. Anisocytosis can be a sign of diseases such as kidney failure or heart failure. However, this blood test cannot be used on its own to diagnose any medical condition, and the result has to be considered in the context of your symptoms and medical history.
This article explains what anisocytosis is, why it happens, and what it means.
Illustration by Zoe Hansen for Verywell Health
Anisocytosis Quick Facts and Terms to Know
Red blood cell distribution width (RDW) defines the variability in size of red blood cells that are measured during a blood test. Typically, your red blood cells are approximately the same size. A significant variability in their size could indicate a problem with your red blood cell production or survival.
Function of Red Blood Cells
Red blood cells travel throughout the body in the arteries, veins, and capillaries. These cells carry oxygen to all of the organs in the body, and they also pick up and carry carbon dioxide waste to the lungs.
Red blood cells survive for about three to four months. You are always making new red blood cells, using recycled material from red blood cells that have undergone programmed degeneration.
Size of Anisocytosis Cells
As part of the CBC blood test, the mean corpuscular volume (MCV) measurement reports the average size of red blood cells in a sample, Normal red blood cells should be about 80 to 100 femtoliter (fl) in volume.
Smaller red blood cells are described as microcytic, and larger red blood cells are described as macrocytic.
RDW reports how varied the red blood cells are in size. Normal RDW should be 12% to 15%. Anisocytosis means that the variability in size is higher than this range.
What Is Poikilocytosis?
Poikilocytosis means a high percentage of abnormally shaped red blood cells. This can be detected with a blood smear. Different diseases and types of anemia can cause poikilocytosis, anisocytosis, or both.
Anisocytosis and Anemia: What to Know
Anemia is low red blood cell count or impaired red blood cell function. Each cause of anemia affects the size and number of red blood cells, but the different causes don’t affect these parameters in the same way.
For example, vitamin B12 deficiency can cause macrocytic anemia, characterized by large red blood cells. Iron deficiency can cause microcytic anemia, characterized by small red blood cells.
Anisocytosis can occur at certain stages of anemia, which is why interpreting this result has to take symptoms and other tests into consideration.
Sometimes, anisocytosis may occur at early stages of anemia, when some healthy red blood cells are still in circulation. As anemia worsens, the unhealthy red blood cells continue to proliferate, and RDW may decrease as the cells become more uniform in size.
Symptoms to Recognize
Anemia has many causes and types, all with similar symptoms.
Anemia symptoms include:
Fatigue
Sleepiness
Pale skin
Low energy
Feeling cold all the time
Dizziness
Rapid heart rate
Shortness of breath
These symptoms can occur with any type of anemia—with or without anisocytosis.
Anisocytosis Unrelated to Anemia
Many diseases can have harmful effects on the production or survival of red blood cells. Anisocytosis often occurs with diseases such as cancer, heart disease, kidney disease, liver disease, and bone marrow disease.
Generally, anisocytosis is not useful in diagnosing these conditions, but it can often indicate how advanced the underlying disorder has become. And sometimes, anisocytosis is an indication of disease prognosis—which means how likely a person is to have a good outcome.
Anisocytosis may also be seen after blood transfusion, as the transfused cells can be a different size than the person's circulating cells.
Test to Diagnose Anisocytosis
The diagnosis of anisocytosis is established with a blood test. A CBC is a routine blood test that is used to examine the size, quantity, concentration, and shape of red blood cells and white blood cells.
If your CBC shows that you have anisocytosis, you will likely need further testing to identify the cause. Additional testing would be directed by your symptoms, medical history, and other test results.
Some tests that you might have to determine the cause of anisocytosis:
Electrolyte blood test
Vitamin B12 level
Chest X-ray
Bone marrow biopsy (removing a sample of marrow for examination in a lab)
Additionally, you will also likely have your blood pressure and pulse checked because anemia can cause low blood pressure and a rapid heart rate. You may also need an evaluation of your heart function, which can include an electrocardiogram (ECG or EKG) or echocardiogram.
Related: Confused About Your Health? The Answer May Be in Your Blood
Treatment for Anisocytosis
Anisocytosis is treated with the same therapeutic interventions that are used to treat anemia. The treatment of anemia is directed toward the underlying cause.
For example, if your anemia is caused by a nutrient deficiency, you would be treated with supplements to provide you with an adequate supply of that nutrient. If your anemia is caused by cancer or kidney disease, the underlying caused would be treated.
During your treatment, you will likely have a repeat CBC blood test to examine your blood count and any changes in your RDW.
Precautions in Special Populations
Sometimes the risk of anemia is higher than usual in certain populations. If you are at risk of anemia, it’s important to get routine medical care so that your healthcare providers will be able to identify and treat early signs of anemia before you start to develop serious complications.
Pregnancy
During pregnancy, there is an increased risk of anemia. Monitoring for anemia is one of the things that you would need during pregnancy prenatal care. Anisocytosis can sometimes be a sign of a higher potential risk of pregnancy complications.
Aging
Aging has been associated with anisocytosis, even without underlying disease. Some research suggests that RDW increases with age could be associated with a higher risk of future disease. Certain protein changes in the body could cause an increase in RDW that's associated with aging.
Follow-Up and Next Steps
It’s possible that you could be at risk of recurrence if you’ve already had anemia. After any therapeutic intervention for anemia, it’s important that you continue your scheduled medical follow-up appointments so that your symptoms, physical signs, and blood tests can be reevaluated at appropriate intervals.
You might need to remain on chronic treatment to prevent your underlying condition from returning. If you develop symptoms of anemia after you’ve been treated, it’s important that you call your healthcare providers to get prompt treatment.
Summary
Anisocytosis is a variability in red blood cell size. This is often a sign of anemia or disease. A variety of medical conditions can lead to anisocytosis, including cancer, liver failure, kidney failure, or nutrient deficiency.
Different types of anemia and other underlying causes of anisocytosis vary in treatment. Diagnosis of the underlying cause determines which treatment will be right for you.
After treatment for the cause of anisocytosis, you need to know when to contact a healthcare provider if you start to develop symptoms of anemia or another underlying condition.
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