What Is Anisocytosis?
Anisocytosis is a term that means your red blood cells (RBCs) vary in size more than usual. They might be smaller or larger than they should be, or a mix of both. Normally, red blood cells are all about the same size. Your doctor might notice this difference when you have a blood test.
Anisocytosis isn't a health condition itself. But it can be a sign that you have one, such as a nutritional deficiency, anemia, or a bone marrow disorder.
Any abnormality of your red blood cells is significant because of the important role these cells play in carrying oxygen to cells all over your body. Scientists are still studying anisocytosis and its relationship with diseases.
Red Blood Cells and What They Do
Red blood cells are the most abundant blood cells in your body. They make up almost half of your blood's volume. They grow in your bone marrow and take about seven days to mature. A hormone called erythropoietin controls the production of your RBCs, which are also known as erythrocytes.
Red blood cells are uniquely suited for their twin jobs. These include carrying oxygen from your lungs to the rest of your body and then returning with the carbon dioxide that you exhale. A protein called hemoglobin inside RBCs transports oxygen and carbon dioxide.
Red blood cells are shaped like disks that are thinner in the middle. They resemble doughnuts without the hole. They don't need a thick middle because they have no nuclei. This shape allows them to fold over so they can fit through your narrowest blood vessels.
The lack of a nucleus means that red blood cells don't live long. Their life span is just four months. They perform such important jobs in your body that abnormalities in their size, shape, and number can seriously affect your health.
Measuring Anisocytosis
Your doctor can see whether you have anisocytosis by doing a complete blood count (CBC) test. In particular, they'll look at a measurement in the CBC called red blood cell distribution width (RDW). A high RDW value means that the variation in the size of your red blood cells is higher than normal. A high RDW value can be caused by cells that are larger than normal, smaller than normal, or both.
A high RDW value doesn't always mean that you're ill. RDW values increase with age and can be higher in certain ethnic groups. They may also increase during the later stages of pregnancy and after physical exercise.
Another test that can identify anisocytosis is a peripheral blood smear (PBS), in which a health care provider examines a sample of your blood under a microscope.
Your doctor will combine the results of these tests with those of other tests to make decisions about your health.
Anisocytosis normal range
A RDW value between 12% and 15% is considered normal. If it's above that, you may have anisocytosis.
Anisocytosis and Poikilocytosis
Anisocytosis and poikilocytosis are both terms that doctors use to describe abnormalities in red blood cells. With anisocytosis, your RBCs are larger or smaller than normal. But with poikilocytosis, more than 10% of your RBCs are shaped abnormally. They might be round, elongated, or crescent-shaped.
Among the causes of poikilocytosis are:
- Inherited disorders, such as sickle cell disease or thalassemia (in which your body makes too few red blood cells)
- Various types of anemia
- Nutrient deficiencies
- Kidney or liver disease
- Poisoning
- Snakebite
It's possible to have both anisocytosis and poikilocytosis. This usually means you have anemia, which means your red blood cells aren't able to carry oxygen as well as they should.
Causes of Anisocytosis
Blood problems known as anemias are the most common cause of anisocytosis. Anemia is when your blood has too few healthy RBCs, meaning your tissues don't get enough oxygen-rich blood. Anemia is not a diagnosis, but a symptom of an underlying problem.
Common signs and symptoms of anemia include:
- Fatigue
- Weakness
- Pallor
- Breathlessness with exertion
Anemia is treated by addressing its cause. Sometimes that means taking supplements or changing your diet. You may need blood transfusions if your level of red blood cells gets too low. Some types of anemia can require a bone marrow transplant.
Anemia is sometimes a symptom of a type of cancer that affects the bone marrow. These cancers include:
- Leukemia
- Lymphoma
- Multiple myeloma
- Myelodysplastic syndromes
It can also be a side effect of cancer treatment.
Kinds of Anemia
You may have anisocytosis with several types of anemia, including:
Iron deficiency anemia. Red blood cells may be abnormally small and pale in this type of anemia. Iron deficiency is most often caused by blood loss. Too little iron in your diet or a problem with absorbing the iron you consume can also cause it.
Vitamin deficiency anemia. A shortage of vitamin B12, folate, or both can cause this anemia. It's also known as megaloblastic anemia because some of the red blood cells are large and abnormally shaped.
Sickle cell anemia. With this inherited condition, your RBCs are crescent- or sickle-shaped. This abnormal shape causes them to die too quickly.
Autoimmune hemolytic anemia. With this condition, your immune system attacks your own RBCs.
Pernicious anemia. This autoimmune condition keeps your body from absorbing enough vitamin B12.
Anemia during pregnancy. You can develop anemia while pregnant because your body needs extra blood to help your fetus grow.
Some kinds of anemia don't have anisocytosis as a symptom. These are called normocytic because the red blood cells are of normal size. An RDW test is still helpful here. It can rule out some types of anemia.
Other Conditions Associated With Anisocytosis
Researchers have discovered that many conditions besides anemia are associated with anisocytosis as measured by an RDW test. In fact, a high RDW value has been linked to a higher overall death rate.
Doctors aren't sure whether anisocytosis plays a role in health deterioration or if it is simply a marker of illness. Is it a cause or an effect? Could it be used more widely in the diagnosis of illness? Can it even predict outcomes? Scientists are interested in these questions.
Other than anemias, some conditions that are associated with anisocytosis include:
Cardiovascular disease. Many people with atrial fibrillation, coronary artery disease, and other heart problems have higher-than-normal RDW scores. This indicates anisocytosis.
Liver disease. One study suggested that RDW could be used to predict three-month death rates in people with liver disease. Another study found that high RDW values were related to poor outcomes from hospitalization.
Kidney disease. In one study of people with acute kidney failure, high RDW scores were identified in people who died within 28 days. A study of patients with kidney disease showed that RDW scores increased as people experienced more serious stages of the disease.
Colorectal cancer. People with colorectal cancer had lower overall survival rates when they had high RDW scores, showing anisocytosis. This was true whether the test was done before surgery or after.
After a blood transfusion, your blood might show signs of anisocytosis. Some drugs could cause it as well.
Anisocytosis FAQs
Which vitamin deficiency causes anisocytosis?
Nutritional deficiencies in vitamin B12, folate (B9), or iron could lead to anisocytosis.
Can leukemia cause anisocytosis?
Leukemia can lead to anemia, which is a known cause of anisocytosis. Some early research in aged rats found that those with advanced leukemia often had anisocytosis. The researchers concluded that anisocytosis could be a sign of leukemia among this group. We need more research into the possible link in humans.
What is anisocytosis of platelets?
Platelet anisocytosis means the platelets in your blood vary in size more than normal. Platelets are cell fragments that are involved in blood clotting.
What is another word for anisocytosis?
Doctors may use the term anisopoikilocytosis when you have both anisocytosis (meaning your RBCs vary in size more than normal) and poikilocytosis (your RBCs are abnormally shaped).
Doctors use these terms to describe specific types of anisocytosis:
- Macrocytosis, in which your RBCs are larger than usual
- Microcytosis, in which your RBCs are smaller than usual
Does COVID cause anisocytosis?
Doctors have found anisocytosis in some people with COVID-19. It's linked to more serious disease and a worse outcome in these people. We need more research into this connection.