From the Guidelines
Elevated MCV is most likely indicative of vitamin B12 or folate deficiency, and a comprehensive workup including complete blood count, reticulocytes, serum ferritin, and vitamin B12 and folic acid levels is necessary for proper diagnosis and management. Elevated MCV (mean corpuscular volume) indicates larger-than-normal red blood cells, a condition called macrocytosis. According to the European Consensus on the Diagnosis and Management of Iron Deficiency and Anaemia in Inflammatory Bowel Diseases 1, macrocytosis may indicate B12 or folate deficiency, and normocytosis with normal or even elevated serum ferritin. The study suggests that the minimum workup should include complete blood count with MCV, reticulocytes, serum ferritin, transferrin saturation, and CRP, and more extensive workup may include vitamin B12, folic acid, haptoglobin, a differential white blood cell count, and bone marrow smear.
Some key points to consider in the evaluation of elevated MCV include:
- The percentage of anaemia of chronic disease (ACD) and the role of inflammation in iron deficiency anaemia
- The usefulness of MCV and mean corpuscular hemoglobin (MCH) as variables in the detection of iron deficiency
- The importance of reticulocyte count in distinguishing between deficiencies and primary bone marrow disease
- The need to estimate serum concentrations of haptoglobin, lactate dehydrogenase, and bilirubin to rule out hemolysis
In terms of management, treatment depends on the underlying cause, and may include vitamin B12 injections or oral supplements, folate supplements, or addressing underlying conditions such as alcohol abuse or hypothyroidism. The normal MCV range is typically 80-100 femtoliters, with values above 100 considered elevated. As noted in the European Consensus 1, a comprehensive list of anaemias classified with MCV and reticulocytes can help guide diagnosis and management.
From the Research
Causes of Elevated MCV
- The most common causes of macrocytosis are drug therapy, alcohol, liver disease, and reticulocytosis 2
- Megaloblastic hematopoiesis, usually caused by vitamin B12 deficiency, accounts for less than 10% of cases 2
- Vitamin B12 or folate deficiency, liver disease, and reticulocytosis are the three most common causes of macrocytosis, and can usually be differentiated based on red cell indexes and morphologic findings 3
- Other possible etiologies include hypothyroidism, primary bone marrow dysplasias, and myeloproliferative disorders 4
Diagnosis of Elevated MCV
- Assessment of complete blood counts, morphologic review, liver function tests, and levels of serum cobalamin, methylmalonic acid, and total homocysteine can help diagnose the cause of macrocytosis 2
- Serum vitamin B12 determination is the best test for unmasking vitamin B12 deficiency, and should be ordered in conjunction with serum and red cell folate determinations 3
- A peripheral smear can indicate megaloblastic anemia, and a reticulocyte count can help differentiate between drug or alcohol toxicity and hemolysis or hemorrhage 4