Megaloblastic anemia

by Rosemarie Tremblay-LeMay MD FRCPC
November 19, 2023


Megaloblastic anemia is a type of anemia caused by low levels of vitamin B12 or folate in the body. Anemia means that the number of red blood cells (RBCs) or the amount of hemoglobin in the blood is lower than normal. RBCs which carry oxygen in your blood require vitamin B12 and folate to develop normally and produce hemoglobin. Cells use vitamin B12 and folate to produce new genetic material (DNA), which is held in a part of the cell called the nucleus.

What are the symptoms of megaloblastic anemia?

Symptoms of megaloblastic anemia include fatigue, shortness of breath, weakness, dizziness, and chest pain. However, some people with megaloblastic anemia will experience no symptoms and the condition will be diagnosed only after blood tests are performed for another reason.

What causes vitamin B12 deficiency?

Vitamin B12 is found in food that comes from animals. The stomach produces a protein called intrinsic factor, a substance that helps the body absorb vitamin B12 in the small intestine. This process also requires substances made by the pancreas. Once absorbed, vitamin B12 is stored in the liver.

Low levels of vitamin B12 can be caused by a lack of vitamin B12 in the diet (for example, a vegan diet without supplementation), diseases involving the stomach, pancreas, or small intestine, and certain medications. Pernicious anemia is a special type of megaloblastic anemia caused by low levels of intrinsic factor, either because it cannot be produced properly or because antibodies destroy it.

What causes folate deficiency?

Folate is a word that describes a group of essential vitamins. Folic acid is a form of folate found in nutritional supplements. Folates are found in fruits and vegetables and are absorbed in the small intestine. Low levels of folate can be caused by a lack of folate in the diet, diseases that prevent absorption in the small intestine, and certain medications. Women who are pregnant or breastfeeding require additional folate and it is recommended that they take supplements. Folate deficiency is rare in developed countries where folate is commonly added to flour.

How is this diagnosis made?

The diagnosis is usually made after blood work shows anemia with large RBCs (macrocytic) or abnormal neutrophils. Additional blood tests will reveal low levels of vitamin B12, or more rarely low levels of folate. Low levels of vitamin B12 or folate prevent RBCs from producing a normal amount of genetic material. This causes the RBC to become abnormally large and have abnormal nuclei. Pathologists call these cells megaloblastic. Other specialized immune cells called neutrophils are often also affected.

Megaloblastic anemia

About this article

This article was written by doctors to help you read and understand your pathology report. Contact us if you have any questions about this article or your pathology report. Read this article for a more general introduction to the parts of a typical pathology report.

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