Macrocytosis is the name for atypically large red blood cells. The condition has many links to other problems, including alcohol use and nutrition. While macrocytosis itself is usually harmless, the responsible conditions may be life-threatening. Interestingly, modern research suggests that macrocytosis may help doctors make difficult diagnoses.


Macrocytosis is not a specific disease but a sign that may result from a variety of conditions and issues. Traditionally, it has close ties to anemia. Some of the other common causes include liver disease, vitamin deficiencies, hypothyroidism, and alcoholism.

Macrocytosis may be a side effect of cancer, seizure, and autoimmune disorder medications. Occasionally, it indicates a serious underlying problem, like bone marrow cancer.

Directly Above Shot Of Alphabets Making Anemia Text By Stethoscope On Table Sohel Parvez Haque / EyeEm / Getty Images


Symptoms of Macrocytosis

In most cases, macrocytosis causes no symptoms and is completely unnoticeable. While some experts attribute symptoms like fatigue, dizziness, and shortness of breath to macrocytosis, others believe it is just one more symptom of the underlying cause.

Research indicates that macrocytosis could lead to neurological issues, like confusion, depression, and atypical sensations in the arms and legs.

woman lying in the couch with her hand on her head Maskot / Getty Images


Discovery and Definition

Because macrocytosis is typically asymptomatic, doctors usually discover the condition incidentally on routine blood tests. Experts define macrocytosis as "having a mean corpuscular volume of over 100 femtoliters." Essentially, this means that the average volume of the red blood cells is significantly higher than is typical. These larger-than-average red blood cells are also called macrocytes or megalocytes.

Close up of nurse disinfecting male arm before blood test. YakobchukOlena / Getty Images


Diagnostic Process

While recognizing macrocytosis is simple, it is important for medical experts to rule out other conditions and identify the underlying cause. This typically begins with a medical history that looks for issues like alcohol use disorder or anemia and includes a physical exam.

Because research links macrocytosis to vitamin deficiencies, doctors may also test B12 serum levels.

Midsection Of Doctor Examining Patient In Hospital Sarinya Pinngam / EyeEm / Getty Images


Vitamin B12 Deficiency and Macrocytosis

Newer findings link B12 deficiency-related macrocytosis with pernicious anemia, a rare autoimmune condition that prevents the body from absorbing vitamin B12.

People who have a B12 deficiency may feel unusual sensations and experience neurological issues like loss of coordination. Macrocytosis is much less common during pregnancy, due to prenatal vitamins often containing folic acid and B12.

woman feeling dizzy at home Pheelings Media / Getty Images


Folate Deficiency and Macrocytosis

Folate, or vitamin B9, deficiency with macrocytosis is similar to B12 deficiency in that it often stems from poor intake or absorption. Many medications that treat seizures, cancer, and autoimmune diseases can cause folate deficiency, which contributes to the associations between the drugs and macrocytosis.

Unlike testing for other nutritional issues, measuring serum folate levels is not useful because they fluctuate rapidly.

Cropped shot of a young woman taking medication at home Jay Yuno / Getty Images


Alcohol Use and Macrocytosis

Researchers note that macrocytosis is somewhat common in patients with no history of anemia or other conditions. One study found that upwards of 80% of males with the symptom and 34% of the women showed signs of alcohol use disorder.

Some of the people with macrocytosis and alcohol use disorder also had notable folate and vitamin B12 deficiencies, which led to dramatically larger red blood cells. It is unclear what the long-term effects of this might be. Additionally, researchers suggest that macrocytosis, along with other tests, may be an effective way of diagnosing alcohol use disorder.

man holding a glass of beer Verity E. Milligan / Getty Images



Doctors will not typically treat macrocytosis itself and will instead focus on discovering and managing the underlying cause. In many cases, no treatment is necessary.

When it is, vitamin injections can help with nutritional deficiencies, as can dietary changes. If medications are causing noticeable side effects, experts may weigh the costs and benefits and recommend a different drug where possible. Blood transfusions may be necessary for patients with severe anemia.

doctor giving injection to patient Ake Ngiamsanguan / Getty Images



A person may be able to lower their risk for macrocytosis by making a few lifestyle changes. The numerous connections between low folate and vitamin B12 levels with macrocytosis means that following a well-balanced diet is key. Visit a healthcare professional regularly to ensure that any underlying conditions are discovered before they can worsen.

Lunchbox with quinoa salad with tomato and cucumber, blue berry and trail mix Westend61 / Getty Images



Because, in most cases, macrocytosis is a sign rather than a condition needing treatment, the prognosis is dependent on the underlying issue. For example, macrocytosis is an expected and common side effect of some medications and typically does not prevent positive outcomes from the treatments.

However, other conditions that cause macrocytosis may lead to long-term neurological issues and symptoms.

woman lying down in bed with hand on her head Westend61 / Getty Images


Popular Now on Facty Health


This site offers information designed for educational purposes only. You should not rely on any information on this site as a substitute for professional medical advice, diagnosis, treatment, or as a substitute for, professional counseling care, advice, diagnosis, or treatment. If you have any concerns or questions about your health, you should always consult with a physician or other healthcare professional.