Macrocytic anaemia- Classification & Causes, Megaloblastic anaemia, Vitamin B12 and Folate deficiency

Macrocytic anaemia

If mean corpuscular volume is more than normal then the anaemia is called macrocytic anaemia.

Classification of macrocytic anaemia:

1. Megaloblastic anaemia

2. Normoblastic macrocytic anaemia.

Megaloblastic anaemia:

An anaemia characterized by appearance of morphologically and functionally abnormal red nucleated red cell precursor called megaloblasts in the bone marrow. These cells give rise to red cells which are also abnormal in size and shape, the most prominent abnormality being macrocytosis.

Causes of megaloblastic anaemia: 

Megaloblastic anaemia occurs due to deficiency of vitamin B12 or folate, or due to therapy with drugs interfering with DNA sysnthsis.

Causes of vitamin B12 deficiency:

1. Decreased intake: occurs in nutritional deficiency.

2. Decreased absorption:

                Gastric cause: Pernicious anaemia, gastrectomy

                Intestinal cause: Lesions of small intestine, Coeliac disease, tropical sprue, fish tape worm infestation

3. Drugs: very rare cause, eg para-aminosalicylic acid

4. Abnormalities of cobalamin metabolism.

Causes of folate deficiency:

1. Decreased intake: Nutritional deficiency

2. Increased absorption: Coeliac disease, Tropical sprue.

3. Increased demand: Pregnancy and puerperium,
                                             Haemolytic anaemia, sideroblastic anaemia,
                                             Leucamia, lymphoma, cancer, myeloproliferative disorders,
                                             Hyperthyroidism, Skin disease

4. Drugs: Folate antagonists (Anti-folate drugs) like methotraxate, trimethoprim, phenytoin

5. Abnormalities of folate metabolism

6. Therapy with drugs interfering with DNA systhesis:

                    Cytosine arabinoside
                    Hydroxyurea
                    6-mercaptourine

Causes of normoblastic macrocytic anaemia:

1. Haemolytic anaemia

2. Post haemorrhagic anaemia / Anaemia due to acute blood loss

3. Aplastic anaemia

4. Acute leukemia

5. Alcoholism

6. Liver disease

7. Sideroblastic anaemia

8. Scurvy

9. Cytotoxic drug therapy

10. Hyperthyroidism

Note : In the making of the above article the follwing books were used:

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