From the Guidelines
Macrocytic anemia should be treated with vitamin B12 supplementation, specifically hydroxocobalamin 1 mg intramuscularly, administered on alternate days until there is no further improvement, then hydroxocobalamin 1 mg intramuscularly administered every 2 months, as recommended by the most recent guidelines 1.
Causes and Treatment
The most common causes of macrocytic anemia include vitamin B12 deficiency, folate deficiency, alcoholism, liver disease, and certain medications.
- Vitamin B12 deficiency is treated with hydroxocobalamin 1 mg intramuscularly, three times a week for 2 weeks, followed by maintenance treatment with 1 mg intramuscularly every 2–3 months for life 1.
- Folic acid deficiency is treated with oral folic acid 5 mg daily for a minimum of 4 months, after excluding vitamin B12 deficiency 1.
Diagnosis and Evaluation
Laboratory evaluation should include:
- Complete blood count
- Peripheral blood smear
- Reticulocyte count
- Vitamin B12 and folate levels
- Liver function tests
- Thyroid function tests Symptoms may include fatigue, weakness, pale skin, shortness of breath, and neurological symptoms in B12 deficiency, such as numbness, tingling, and difficulty walking.
Importance of Prompt Treatment
Prompt diagnosis and treatment are essential to prevent complications such as irreversible neurological damage in cases of B12 deficiency or worsening anemia that can strain the cardiovascular system. The treatment approach should prioritize the underlying cause of the macrocytic anemia, and the most recent guidelines should be followed to ensure the best possible outcomes for patients 1.
From the FDA Drug Label
Impairment of thymidylate synthesis in patients with folic acid deficiency is thought to account for the defective deoxyribonucleic acid (DNA) synthesis that leads to megaloblast formation and megaloblastic and macrocytic anemias. The answer to the question about macrocytic anemia is that folic acid deficiency can lead to macrocytic anemia due to impaired thymidylate synthesis and defective DNA synthesis, resulting in megaloblast formation. Key points include:
- Megaloblastic anemia is associated with folic acid deficiency
- Macrocytic anemia is a type of anemia that can occur due to folic acid deficiency
- Folic acid is necessary for normal erythropoiesis and nucleoprotein synthesis 2
From the Research
Definition and Classification of Macrocytic Anemia
- Macrocytic anemia is defined as a red blood cell (RBC) mean corpuscular volume (MCV) >100 femtoliter (fL) 3.
- Macrocytic anemias are generally classified into megaloblastic or nonmegaloblastic anemia 3.
- Megaloblastic anemia is caused by deficiency or impaired utilization of vitamin B12 and/or folate, whereas nonmegaloblastic macrocytic anemia is caused by various diseases such as myelodysplastic syndrome (MDS), liver dysfunction, alcoholism, hypothyroidism, certain drugs, and by less commonly inherited disorders of DNA synthesis 3.
Causes and Diagnosis of Macrocytic Anemia
- The three most common causes of macrocytosis are vitamin B12 or folate deficiency, liver disease, and reticulocytosis, which can usually be differentiated on the basis of red cell indexes and morphologic findings 4.
- Serum vitamin B12 determination remains the best test for unmasking vitamin B12 deficiency, and should be ordered in conjunction with serum and red cell folate determinations in the course of investigating a macrocytic anemia 4.
- Megaloblastic anemia can be diagnosed based on characteristic morphologic and laboratory findings, but other benign and neoplastic diseases need to be considered, particularly in severe cases 5.
Treatment and Outcome of Macrocytic Anemia
- Macrocytic anemias are treated with cause-specific therapies, and it is crucial to differentiate nonmegaloblastic from megaloblastic anemia 3.
- Therapy involves treating the underlying cause, such as with vitamin supplementation in cases of deficiency, or with discontinuation of a suspected medication 5.
- Folate and B12 deficiencies may result in macrocytic anemia, and are common in major depression; hypofolatemia may result in poorer antidepressant response 6.
- Low vitamin B-12 status is associated with anemia, macrocytosis, and cognitive impairment in older Americans, and high serum folate may exacerbate these effects in individuals with low vitamin B-12 status 7.