Macrocytic anemia happens when you have large red blood cells and not enough normal-sized red blood cells. It can result from a vitamin deficiency or an underlying condition like hypothyroidism.


Macrocytosis is a term used to describe red blood cells that are larger than normal. Anemia is when you have low numbers of properly functioning red blood cells in your body. Macrocytic anemia, then, is a condition in which your body has overly large red blood cells and not enough normal red blood cells.

Different types of macrocytic anemia can be classified depending on what’s causing it. Most often, macrocytic anemias are caused by a lack of vitamin B-12 and folate. Macrocytic anemia can also signal an underlying condition.

You may not notice any symptoms of macrocytic anemia until you’ve had it for some time.

Symptoms include:

  • loss of appetite or weight
  • brittle nails
  • fast heartbeat
  • diarrhea
  • fatigue
  • pale skin, including lips and eyelids
  • shortness of breath
  • poor concentration or confusion
  • memory loss

If you have several of these symptoms, make an appointment to see your doctor.

It’s important to make an appointment as soon as possible if you have the following symptoms:

  • increased heart rate
  • confusion
  • memory problems

Macrocytic anemia can be broken into two main types: megaloblastic and nonmegaloblastic macrocytic anemias.

Megaloblastic macrocytic anemia

Most macrocytic anemias are also megaloblastic. Megaloblastic anemia is a result of errors in your red blood cell DNA production. This causes your body to make red blood cells incorrectly.

Possible causes include:

Nonmegaloblastic macrocytic anemia

Nonmegaloblastic forms of macrocytic anemia may be caused by a variety of factors. These can include:

Your doctor will ask about your medical history and lifestyle. They may also ask about your eating habits if they think that you have a type of anemia. Learning about your diet can help them find out if you are deficient in iron, folate, or any of the other B vitamins.

Blood tests

Your doctor will order blood tests to check for anemia and enlarged red blood cells. If your complete blood count indicates anemia, your doctor will do another test known as a peripheral blood smear. This test can help spot early macrocytic or microcytic changes to your red blood cells.

Additional blood tests can also help find the cause of your macrocytosis and anemia. This is important because treatment depends on the underlying cause.

While nutrient deficiencies cause most macrocytic anemias, other underlying conditions may cause the deficiencies. Your doctor will run tests to check your nutrient levels. They may also do blood tests to check for alcohol use disorder, liver disease, and hypothyroidism.

Your primary care doctor may also refer you to a hematologist. Hematologists specialize in blood disorders. They can diagnose the cause and specific type of your anemia.

Treatment for macrocytic anemia focuses on treating the cause of the condition. The first line of treatment for many people is correcting nutrient deficiencies. This can be done with supplements or foods like spinach and red meat. You may be able to take supplements that include folate and other B vitamins. You may also need vitamin B-12 injections if you don’t absorb oral vitamin B-12 properly.

Foods high in vitamin B-12 include:

  • chicken
  • fortified grains and cereals
  • eggs
  • red meat
  • shellfish
  • fish

Foods high in folate include:

  • dark leafy greens, such as kale and spinach
  • lentils
  • enriched grains
  • oranges

Most cases of macrocytic anemia that are caused by vitamin B-12 and folate deficiencies can be treated and cured with diet and supplements.

However, macrocytic anemias can cause long-term complications if left untreated. These complications can include permanent damage to your nervous system. Extreme vitamin B-12 deficiencies may cause long-term neurologic complications. They include peripheral neuropathy and dementia.

You can’t always prevent macrocytic anemia, particularly when it’s caused by underlying conditions out of your control. However, you can prevent the anemia from becoming severe in most cases. Try these tips:

For healthier red blood cells

  • Add more red meat and chicken to your diet to increase your vitamin B-12 intake.
  • If you’re a vegetarian or vegan, you can add beans and dark, leafy greens for folate. Try fortified breakfast cereals for vitamin B-12.
  • Reduce the amount of alcohol you drink.
  • Talk to your doctor if you take antiretrovirals for HIV, antiseizure medications, or chemotherapy drugs. These may increase your risk of developing macrocytic anemia.
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