From the Guidelines
The next steps in managing a patient with macrocytosis involve checking vitamin B12 and folate levels to identify potential deficiencies, and treating them accordingly, as these are the most common causes of macrocytic anemia. To manage a patient with macrocytosis, the following steps should be taken:
- Obtain a detailed history focusing on alcohol use, medication review, dietary habits, and family history.
- Order comprehensive laboratory tests including complete blood count with peripheral smear, vitamin B12 and folate levels, thyroid function tests, liver function tests, reticulocyte count, and serum lactate dehydrogenase.
- If vitamin B12 deficiency is confirmed, treat 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.
- For folic acid deficiency, prescribe oral folic acid 5 mg daily for a minimum of 4 months 1.
- If alcoholism is the cause, recommend alcohol cessation and nutritional supplementation.
- For drug-induced macrocytosis, consider medication alternatives when possible.
- In cases where initial testing is inconclusive and macrocytosis persists, bone marrow examination may be necessary to rule out myelodysplastic syndrome or other hematologic disorders. It is essential to note that vitamin B12 deficiency should be treated immediately, especially if there is possible neurological involvement, and urgent specialist advice should be sought from a neurologist and haematologist 1.
From the FDA Drug Label
DOSAGE AND ADMINISTRATION Pernicious Anemia Parenteral Vitamin B12 is the recommended treatment and will be required for the remainder of the patient's life. A dose of 100 mcg daily for six or seven days should be administered by intramuscular or deep subcutaneous injection. If there is clinical improvement and if a reticulocyte response is observed, the same amount may be given on alternate days for seven doses, then every three to four days for another two to three weeks. By this time hematologic values should have become normal This regimen should be followed by 100 mcg monthly for life. Folic acid should be administered concomitantly if needed.
The patient has macrocytosis (indicated by MCV of 101 fL) which may be due to a vitamin deficiency, such as Vitamin B12 deficiency.
- The next steps in managing this patient would be to:
- Administer Vitamin B12 (cyanocobalamin) 100 mcg daily for 6-7 days via intramuscular or deep subcutaneous injection, as per the dosage recommendations for pernicious anemia 2.
- Monitor for clinical improvement and reticulocyte response.
- Consider administering folic acid concomitantly if needed, but ensure that Vitamin B12 deficiency is ruled out or being adequately treated with cobalamin 3.
From the Research
Next Steps in Managing a Patient with Macrocytosis
The patient's lab results show a mean corpuscular volume (MCV) of 101 fL, which is higher than the normal range of 79-97 fL, indicating macrocytosis. The following steps can be taken to manage the patient:
- Obtain a detailed history and physical examination to identify potential causes of macrocytosis, such as alcoholism, vitamin B12 and folate deficiencies, and medications 4, 5.
- Order laboratory tests, including:
- Vitamin B12 level to check for deficiency 4, 6, 7.
- Reticulocyte count to differentiate between drug or alcohol toxicity and hemolysis or hemorrhage 4.
- Peripheral smear to check for megaloblastic anemia or other abnormalities 4, 6.
- Serum folate level to check for deficiency 6, 7.
- Liver function tests (LFTs) to check for liver disease 7, 5.
- Thyroid function tests (TFTs) to check for hypothyroidism 7, 5.
- Consider bone marrow biopsy and cytogenetic analysis if the diagnosis is still unclear after initial evaluation 5, 8.
- Follow-up with blood cell counting every 6 months for patients with unexplained macrocytosis, and consider bone marrow biopsy if cytopenias are present 8.
Potential Causes of Macrocytosis
The potential causes of macrocytosis include: