From the Guidelines
A high mean corpuscular volume (MCV) of 111 fL indicates macrocytosis and requires a systematic workup, starting with a thorough history and laboratory tests including complete blood count with peripheral smear, vitamin B12 and folate levels, thyroid function tests, liver function tests, reticulocyte count, and serum LDH, as recommended by the most recent guidelines 1. The workup for macrocytosis should focus on identifying the underlying cause, which can include vitamin B12 or folate deficiency, alcoholism, liver disease, myelodysplastic syndrome, and certain medications.
- Key laboratory tests to order include:
- Complete blood count with peripheral smear
- Vitamin B12 and folate levels
- Thyroid function tests
- Liver function tests
- Reticulocyte count
- Serum LDH
- Consider testing for methylmalonic acid and homocysteine levels if B12 deficiency is suspected despite normal serum B12, as suggested by 1 and 1.
- The most common causes of macrocytosis are vitamin B12 or folate deficiency, alcoholism, liver disease, myelodysplastic syndrome, and certain medications, as noted in 1 and 1.
- If B12 deficiency is confirmed, treat with cyanocobalamin 1000 mcg intramuscularly daily for one week, then weekly for one month, followed by monthly injections or high-dose oral supplementation (1000-2000 mcg daily), as recommended by 1.
- For folate deficiency, prescribe folic acid 1-5 mg daily, as suggested by 1.
- Address underlying causes such as alcoholism or medication effects, and consider hematology consultation for bone marrow examination to rule out myelodysplastic syndrome or other hematologic disorders if initial workup is negative, as recommended by 1.
From the Research
Workup of MCV 111
The workup of a mean corpuscular volume (MCV) of 111 involves several steps to determine the underlying cause of macrocytosis.
- The most common etiologies of macrocytosis are alcoholism, vitamin B12 and folate deficiencies, and medications 2.
- A peripheral smear can help differentiate between megaloblastic and non-megaloblastic anemia, with megaloblastic anemia characterized by macro-ovalocytes and hyper-segmented neutrophils 2, 3.
- Vitamin B12 and folate levels should be checked to rule out deficiencies, as these are common causes of megaloblastic anemia 2, 3, 4.
- A reticulocyte count can help differentiate between drug or alcohol toxicity and hemolysis or hemorrhage 2.
- Other possible etiologies of macrocytosis include hypothyroidism, liver disease, and primary bone marrow dysplasias, such as myelodysplasia and myeloproliferative disorders 2, 4.
Diagnostic Approach
- The diagnostic approach to macrocytosis involves a combination of laboratory tests and physical examination 2, 4.
- The MCV value can help guide the diagnostic workup, but it should not be used as the sole criterion for ruling out certain etiologies 5.
- A broader set of laboratory tests, including vitamin B12 and folate levels, reticulocyte count, and peripheral smear, should be used to determine the underlying cause of macrocytosis 2, 3, 4, 5.