Merck Manual

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Vitamin Deficiency Anemia

(Megaloblastic Anemia)

By

Evan M. Braunstein

, MD, PhD, Johns Hopkins School of Medicine

Last full review/revision Sep 2020| Content last modified Sep 2020
Click here for the Professional Version

Vitamin deficiency anemia results from low or depleted levels of vitamin B12 or folate (folic acid).

  • People may be weak, short of breath, and pale.

  • Nerves may malfunction.

  • Blood tests can detect abnormal cells that indicate vitamin deficiency anemia.

  • The deficient vitamin is replaced.

(See also Overview of Anemia.)

Vitamin B12 deficiency and folate (folic acid) deficiency cause megaloblastic anemia. In megaloblastic anemia, the bone marrow produces red blood cells that are large and abnormal (megaloblasts).

Deficiency of vitamin B12 or folate deficiency most often develops due to a lack of these vitamins in the diet or an inability to absorb these vitamins from the digestive tract. Deficiency of folate (folic acid) is sometimes caused by drugs used to treat cancer.

Symptoms

Symptoms of anemia due to vitamin B12 deficiency or folate deficiency develop slowly and are similar to symptoms caused by other types of anemia, such as fatigue, weakness, and paleness. Vitamin B12 deficiency can also cause nerves to malfunction, causing tingling, loss of sensation, and muscle weakness. Severe vitamin B12 deficiency may cause confusion. In older people, anemia caused by vitamin B12 deficiency may be mistaken for dementia because of this symptom.

Diagnosis

  • Blood tests

Once blood tests show a person has anemia, tests are done to determine if a deficiency of vitamin B12 or folate is the cause. Anemia due to vitamin B12 or folate deficiency is suspected when large (macrocytic) red blood cells and multilobed (hypersegmented) neutrophils (a type of white blood cell) are seen in a blood sample that is examined under a microscope. Reduction in the number of white blood cells and platelets also can occur, especially when people have had vitamin deficiency anemia for a long time.

The blood levels of vitamin B12 and folate are measured, and other tests may be done to determine the cause of the vitamin B12 deficiency.

Treatment

  • Replacement of vitamin B12 or folate

The treatment of anemia due to vitamin B12 deficiency or folate deficiency consists of replacing the deficient vitamin.

Commonly, vitamin B12 is administered by injection, particularly when the deficiency is severe or caused by an inability to absorb the vitamin from the digestive tract. At first, injections are given daily or weekly for several weeks until the blood levels of vitamin B12 return to normal. Then injections are given once a month. Vitamin B12 can also be taken daily as a nose spray, a tablet placed under the tongue, or a tablet that is swallowed. People who have anemia due to vitamin B12 deficiency may need to take vitamin B12 supplements for life.

Folic acid can be taken as one tablet daily.

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