What Is Microcytic Anemia?

Small red blood cells can cause symptoms of anemia

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Microcytic anemia is a condition in which your red blood cells are too small. Because red blood cells carry oxygen throughout the body, this condition can cause fatigue and low energy. It may develop due to low iron levels or other medical problems.

While microcytic anemia can be diagnosed with a blood test, identifying the cause may require additional diagnostic tests, such as imaging studies or invasive tests like a colonoscopy (a flexible tube with a camera that's used to view the large intestine and rectum) or endoscopy (a flexible tube with a camera that's used to view the digestive tract or other sites inside the body).

Treatment can involve iron supplements or managing the underlying medical cause. This article describes what it’s like to have microcytic anemia and what you can do about it if you have it. 

What to Know About Microcytic Anemia - illustration by Michela Buttignol

Verywell / Michela Buttignol

Types 

There are several types of microcytic anemia. Each of these conditions makes it difficult for the body to produce healthy red blood cells. 

The most common types of microcytic anemia are:

  • Iron deficiency: You can get this mineral by eating meat, fish, beans, leafy green vegetables, and chicken. You can become deficient if you don't consume enough iron-rich foods or you have difficulty absorbing iron in the gastrointestinal system (digestive tract, ranging from the mouth to the anus). Blood loss also causes the body to lose iron and to have low iron levels. 
  • Chronic disease: Many illnesses can make it difficult for the body to produce red blood cells. This can cause microcytic anemia or normocytic (normal size red blood cells) anemia.
  • Lead toxicity: Lead toxicity can occur when a person is exposed to lead in the environment, usually through water contamination or from lead-based paint. This tends to have a more severe effect on children.
  • Thalassemia: This hereditary condition is a genetic defect that affects formation of hemoglobin, a component of the red blood cells. 
  • Sideroblastic anemia: This condition is characterized by sideroblasts in the bone marrow, which are a type of premature red blood cell. Sideroblastic anemia can be acquired and there are hereditary forms as well. It occurs due to dysfunction in the way the body uses iron to make hemoglobin.
  • Vitamin B6 deficiency: This vitamin, which you can get by eating meat, fish, chicken, turkey, and chickpeas, is needed for production of red blood cells. A deficiency can occur due to lack of vitamin B6 in the diet, problems with absorption in the digestive system, or excessive alcohol use.

Sometimes these types overlap, or you can have more than one type. For example, sideroblastic anemia can occur due to lead toxicity. 

Symptoms of Microcytic Anemia 

The symptoms of microcytic anemia develop over time. They tend to be vague and not specifically unique to anemia. 

Symptoms can include:

  • Fatigue, low energy, sleepiness, and sluggishness 
  • General weakness 
  • Pale skin 
  • Dizziness 
  • Headaches 
  • Irritability 
  • Difficulty concentrating 
  • Enlargement of the spleen, which may make the abdomen appear larger

You can have all or some of these symptoms, with varying levels of severity. More severe anemia tends to cause more severe symptoms.

Severity

Other factors can influence the severity of the symptoms of microcytic anemia—such as underlying medical conditions.

What Causes Microcytic Anemia? 

Microcytic anemia occurs when the body cannot make red blood cells of normal size. This can happen if you are deficient in certain components of the red blood cells or can occur due to illnesses that prevent proper red blood cell development.

Conditions that commonly cause microcytic anemia include:

  • Not getting enough iron or vitamin B6 in your diet 
  • Not being able to absorb enough of the iron or vitamin B6 that you eat 
  • Chronic bleeding, such as due to gastrointestinal disease 
  • Acute bleeding, such as due to trauma 
  • Genetic blood disease 
  • Chronic health conditions (such as cancer) that prevent the red blood cells from properly developing
  • Some medications that can cause microcytic anemia as a side effect 

How Microcytic Anemia Develops 

Red blood cells usually last for about 120 days, and your body is constantly making new red blood cells. Hemoglobin, an iron-containing protein, is an important component of red blood cells.

The oxygen that enters your lungs binds to hemoglobin in your red blood cells. It is transported by blood vessels throughout the body to keep your organs and tissues functioning. 

When iron or hemoglobin levels are low, the red blood cells don’t develop as they should, and they don’t carry oxygen efficiently. Hemoglobin is red, and the small red blood cells may also be hypochromic (pale) in color.

Iron deficiency is one of the factors that can cause this problem. Iron is also lost due to acute bleeding—and it can take weeks for your diet or supplements to restore the lost iron. Chronic bleeding makes it hard for a body to replenish its iron supply, and this can lead to persistent microcytic anemia.

Thalassemia causes a defect in the production of hemoglobin. Lead toxicity causes hemolysis (destruction of the red blood cells).

Chronic diseases can cause hemolysis and may also interfere with red blood cell production and iron metabolism. And sideroblastic anemia interferes with the way the body uses iron to make red blood cells.

How Microcytic Anemia Is Diagnosed 

Microcytic anemia can cause signs that are detected on a physical examination, but it doesn’t always do so. Microcytic anemia is diagnosed with blood tests. Sometimes, additional specific blood tests are used to determine the cause. 

Mycrocytic anemia is sometimes detected during examinations and testing for other conditions or during a routine physical. Your healthcare provider may notice signs such as pale skin, a weak pulse, low blood pressure, a rapid heart rate, or splenomegaly (enlarged spleen).

Often, a complete blood count (CBC) is part of a routine medical checkup, and it is frequently ordered if there are any signs or symptoms of anemia. Other blood tests that you might need for further evaluation of microcytic anemia include a blood smear, iron tests, genetic tests, or tests for lead levels. Additional diagnostic tests are sometimes needed.

Blood tests include:

Other Diagnostic Tests 

Sometimes microcytic anemia is caused by bleeding or chronic disease. If this is a possibility for you, your doctor may order additional diagnostic tests to identify the cause of your anemia. 

Tests you might need include:

  • Urinalysis: This is testing a sample of urine. It can identify blood in the urine, which is one sign of hemolysis or bleeding.
  • Imaging tests: If there is concern about cancer or a structural cause of bleeding, an imaging test such as an ultrasound can help visualize it.
  • Colonoscopy: This invasive test can identify sources of bleeding in the intestines.
  • Endoscopy: This invasive test can identify bleeding, cancer, or ulcers in the esophagus or the stomach.
  • Bone marrow biopsy: A bone marrow biopsy may be needed if there is concern about bone marrow disease or bone marrow cancer. A needle is used to take marrow from a bone to be examined in a lab.

Your medical history, family history, symptoms, physical examination, and blood tests would be used to determine which, if any, of these diagnostic tests you might need. 

What Are the Treatments for Microcytic Anemia? 

There are many different treatments for microcytic anemia. Some treatments are used to help resolve the symptoms, and other treatments are used to help your body produce normal red blood cells. 

A blood transfusion may be necessary to alleviate the effects of severe anemia. This can resolve your anemia if it developed due to an acute event, such as blood loss from trauma or surgery. For chronic conditions, repeat blood transfusions may be needed. 

Other treatments are focused on alleviating the cause of the anemia. 

Examples of treatments include:

  • Surgical repair of a bleeding wound
  • Iron replacement 
  • Vitamin B6 supplements
  • Treatment of an underlying illness, such as cancer 
  • Treatment of lead toxicity 
  • Management of thalassemia to avoid complications of the condition

Prognosis: What to Expect 

Microcytic anemia can improve with treatment. It may take weeks or months for you to feel better and for your blood tests to show improvement. Depending on the cause, you may need to continue long-term treatment to prevent microcytic anemia from recurring.

For example, if you have a problem absorbing iron from your diet, you may need to continue to take supplements so you can avoid becoming anemic again. And if you have thalassemia, you would need a long-term treatment regimen.

Summary 

Microcytic anemia describes a condition in which the red blood cells are small. This can occur due to several causes, including nutritional deficiency, hereditary conditions, acute or chronic bleeding, or chronic disease. Microcytic anemia causes nonspecific symptoms. The diagnosis relies on blood tests.

Assessment of the cause is important because the cause guides treatment. Usually, treatment can normalize the red blood cells and alleviate symptoms, but sometimes treatment needs to be maintained long-term. 

A Word From Verywell 

If you have microcytic anemia, it’s important that you follow through with a comprehensive diagnosis and get the treatment you need. While it requires medical care, microcytic anemia is usually treatable, and having this condition doesn’t limit your everyday activities.

With treatment, you will gradually notice that you have more energy and fewer symptoms of anemia. Medical care will also make you more aware of symptoms to look for in the future.

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