Megaloblastic Anemias


Megalosblastic anemias are characterized by the presence of enlarged red cells (megaloblasts) due to the impaired cell division. Because the erythrocytes that reach the circulation are enlarged, a macrocytic and normochromic anemia results.



  • Vitamin B12 deficiency
  • Folic acid deficiency

Vitamin B12 and Folic acid are essential for normal DNA synthesis of erythrocyte formation. When these vitamins are deficient erythrocyte’s DNA synthesis is affected. Mitosis in the progenitor lines is suppressed and abnormal increase in the number of normal cells or hyperplasia occurs. Since there is no impairment of the RNA or protein synthesis cell growth still proceeds. However, because mitosis or cell division can’t occur (because of the absence of Vitamin B12 and Folic Acid) the marrow precursors (erythroid and myeloid cells) remain enlarged which are termed as MEGALOBLASTS. Many of these cells die within the marrow so the mature cells that leave the marrow is decreased in number. As a result, pancytopenia (deficiency of all cellular elements of the blood) develops.

Types of megaloblastic anemia

Vitamin B12 deficiency

Vitamin B12, also known as cobalamin, is not synthesized in the tissues. Thus, the body relies on the dietary intake of meat, liver, seafood and dairy products to supply our needs. The body stores more than a 3-year supply of vitamin B12 in the liver.


  1. Inadequate dietary intake
  2. Impaired gastrointestinal absorption (absence of intrinsic factor, pernicious anemia, gastrectomy, chronic gastritis)

Clinical Manifestations:

  1. Weakness
  2. Listless
  3. Pale
  4. Smooth sore red tongue and diarrhea (those with pernicious anemia)
  5. Neurologic manifestations (confusion, paresthesia, paralysis, severe neuropathy)

Diagnostic evaluation:

  • Schilling test (to determine the cause of Vitamin B12 deficiency)


Vitamin B12 replacement

  • Oral supplementation if the cause is inadequate cobalamin intake.
  • In cases of defective absorption or absence of intrinsic factor, replacement is by intramuscular (IM) injection of Vitamin B12.

Folic Acid Deficiency

Folic Acid is another vitamin that is necessary for normal red blood cell production. It is stored in the body as folates. The dietary sources of folate are meats, eggs and leafy vegetables. Body stores of folic acid provide a five-month period of tolerance from proven deficient folic acid in the diet.


  1. Inadequate folate in the diet
  2. Alcoholism (alcohol increases folic acid requirements in the body)

Clinical Manifestations:

Symptoms of folic acid and Vitamin B12 deficiency are the same however, neurologic manifestations of Vitamin B12 deficiency do not occur when folic acid is deficient.


  1. Nutritious diet
  2. Administration of 1 mg folic acid a day (oral)
  3. For patients with malabsorption, folic acid is administered intramuscularly (IM)

image from

Daisy Jane Antipuesto RN MN

Currently a Nursing Local Board Examination Reviewer. Subjects handled are Pediatric, Obstetric and Psychiatric Nursing. Previous work experiences include: Clinical instructor/lecturer, clinical coordinator (Level II), caregiver instructor/lecturer, NC2 examination reviewer and staff/clinic nurse. Areas of specialization: Emergency room, Orthopedic Ward and Delivery Room. Also an IELTS passer.

What Do You Think?