Macrocytosis: What causes it?

The condition of red blood cells that are larger than usual is called macrocytosis. Macrocytosis most often has no symptoms. It’s found on routine blood tests.

Macrocytosis isn’t a disease. But it may mean there’s an underlying condition that needs medical attention. Common causes of macrocytosis include:

• Too little vitamin B-12.
• Too little vitamin folate.
• Liver disease.
• Alcohol use.
• An underactive thyroid, also called hypothyroidism.
• A side effect of certain medicines, such as those used to treat cancer, seizures and conditions in which the body attacks its own cells, called autoimmune hemolytic anemia.
• The spongy tissue inside the bones, called bone marrow, making more red blood cells called reticulocytes to correct anemia. This might happen after blood loss.
• A bone marrow cancer called myelodysplastic syndrome.

If you have macrocytosis, blood tests can help find its cause. Diagnosis may involve taking a sample of the spongy tissue inside the bones, called bone marrow, for testing.

Managing macrocytosis involves treating the cause. If you don’t have enough vitamin B-12 or folate, treatment may include changing your diet. You also might take dietary supplements or get shots to replace the vitamins. If you have serious anemia, you might need to get blood from a donor, called a transfusion.