From the Guidelines
Macrocytic anemia should be treated with vitamin B12 supplementation if deficiency is present, using 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 Diagnosis
Macrocytic anemia is a blood disorder characterized by abnormally large red blood cells and insufficient hemoglobin levels. The most common causes include:
- Vitamin B12 deficiency
- Folate deficiency
- Alcoholism
- Liver disease
- Certain medications Diagnosis involves a complete blood count showing elevated mean corpuscular volume (MCV) above 100 fL, along with peripheral blood smear examination and specific tests for B12 and folate levels.
Treatment
Treatment depends on the underlying cause:
- B12 deficiency typically requires intramuscular injections of hydroxocobalamin, with a dose of 1 mg administered on alternate days until there is no further improvement, then 1 mg administered every 2 months 1.
- Folate deficiency is treated with oral folic acid 5 mg daily for a minimum of 4 months, after excluding vitamin B12 deficiency 1.
- Patients should also address contributing factors like alcohol consumption or medication use.
Monitoring and Prevention
Symptoms like fatigue, weakness, and neurological manifestations (in B12 deficiency) typically improve with treatment, though neurological damage may be permanent if treatment is delayed. Regular monitoring of blood counts and nutrient levels is essential to ensure adequate response to therapy and prevent recurrence. Key points to consider in the treatment of macrocytic anemia include:
- Immediate treatment of vitamin B12 deficiency is crucial to prevent neurological damage 1.
- Folate supplementation may mask severe vitamin B12 depletion, and therefore, vitamin B12 deficiency should be treated immediately before initiating additional folic acid 1.
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) 2
- Macrocytic anemias are generally classified into megaloblastic or nonmegaloblastic anemia 2
- 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 2
Causes of Macrocytic Anemia
- The most common causes of macrocytic anemias in adults are: + Alcoholism + Liver diseases + Hemolysis or bleeding + Hypothyroidism + Folate or vitamin B12 deficiency + Exposure to chemotherapy and other drugs + Myelodysplasia 3
- Vitamin B12 or folate deficiency, liver disease, and reticulocytosis are the three most common causes of macrocytosis, which can usually be differentiated on the basis of red cell indexes and morphologic findings 4
Diagnosis and Evaluation of Macrocytic Anemia
- A carefully obtained history and examination with evaluation of a peripheral blood smear and reticulocyte count should be performed in most patients with macrocytosis 3
- Serum vitamin B12 and folate levels, serum thyroid studies, liver function studies, and bone marrow aspirate and biopsy with cytogenetic analysis are frequently required to confirm a diagnosis suspected on the basis of the initial evaluation 3
- 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
Role of Vitamin B12 and Folate in Macrocytic Anemia
- Low vitamin B12 status is significantly associated with anemia and macrocytosis, and determining a hematologic cutoff value may help physicians in clinical practice 5
- Lack of vitamin-B12 and/or folate with elevated homocysteine is the key factor responsible for megaloblastic anemia, and p53 expression could be used as a surrogate marker for confirming the VB9 and VB12 induced megaloblastic anemia 6