From the Guidelines
An increase in Mean Corpuscular Volume (MCV) within 6 months is most likely caused by vitamin B12 or folate deficiency, as indicated by the European Consensus on the Diagnosis and Management of Iron Deficiency and Anaemia in Inflammatory Bowel Diseases 1. This condition can be diagnosed by considering the patient's complete blood count, reticulocyte count, and serum ferritin levels.
- The MCV and mean corpuscular hemoglobin (MCH) are useful variables in detecting iron deficiency and anaemia.
- A low or normal reticulocyte count may indicate an inability to respond properly to anaemia, either due to deficiencies or primary bone marrow disease.
- Increased reticulocytes, on the other hand, may indicate increased red cell formation, excluding deficiencies and suggesting hemolysis. Key factors to consider in the diagnosis and management of increased MCV include:
- Vitamin B12 and folate deficiency, which can be treated with supplementation, typically 1000 mcg of vitamin B12 daily or 1 mg of folate daily, depending on the deficiency.
- Other potential causes, such as alcohol abuse, hypothyroidism, or reticulocytosis, which may require additional testing and treatment.
- The importance of distinguishing between iron deficiency anaemia and anaemia of chronic disease (ACD) in patients with inflammatory bowel diseases, as the choice of treatment depends on this distinction, as noted in the European Consensus 1.
From the FDA Drug Label
DOSAGE AND ADMINISTRATION ... By this time hematologic values should have become normal The reason for an increase in Mean Corpuscular Volume (MCV) within 6 months is not directly stated in the drug label. Key points:
- The label discusses treatment of vitamin B12 deficiency and pernicious anemia.
- It mentions that hematologic values should become normal after treatment, but does not specify the reason for an increase in MCV. 2
From the Research
Causes of Increased Mean Corpuscular Volume (MCV)
- Vitamin B12 deficiency is a common cause of increased MCV, as seen in studies 3, 4
- Folate deficiency can also lead to increased MCV, as noted in study 5
- Certain medications, such as antiepileptic drugs, can interact with folate and vitamin B12 serum levels, leading to increased MCV 6
- Hydroxychloroquine therapy with methotrexate has been associated with an increase in MCV, which may be a biomarker of treatment response 7
- Alcoholism is also a significant cause of macrocytosis, accounting for 36.5% of cases in one study 4
Factors Influencing MCV
- Population characteristics, such as age and sex, can influence MCV levels 3, 5
- Cut-off levels of MCV and serum vitamin B12 can impact the diagnosis of vitamin B12 deficiency 3
- The use of folic acid fortification has been associated with improved hemoglobin and hematocrit values, as well as a decrease in the prevalence of anemia 5
Clinical Implications
- An elevated MCV can be an indicator of underlying pathology, such as vitamin B12 or folate deficiency, and should be further evaluated 3, 4
- The MCV should not be used as the only parameter to rule out the diagnosis of vitamin B12 deficiency 3
- Treatment with certain medications, such as antiepileptic drugs, should be monitored for potential interactions with folate and vitamin B12 serum levels 6