The Mean Corpuscular Volume (MCV) is a measurement in a standard complete blood count that reflects the average size of red blood cells. An elevated MCV, known as macrocytosis, indicates cells are larger than normal, typically above 100 femtoliters (fL). Normalizing this measurement requires addressing the underlying cause of the cell enlargement, which can range from nutritional deficiencies to complex systemic issues.
Understanding Elevated MCV
An elevated MCV value is a laboratory finding, a symptom, rather than a stand-alone medical diagnosis, which means that effective lowering depends entirely on identifying the root cause. Causes of macrocytosis are broadly categorized based on the mechanism of red blood cell enlargement.
One primary category is megaloblastic macrocytosis, which results from impaired DNA synthesis within the bone marrow. This defect causes the red blood cell precursors to grow larger without dividing properly, leading to the release of oversized cells into the bloodstream. The most common causes of this type are deficiencies in Vitamin B12 and folate, both of which are cofactors required for healthy DNA replication.
The second category is non-megaloblastic macrocytosis, where cell enlargement occurs through pathways that do not involve a DNA synthesis defect. Causes include the toxic effects of substances like alcohol, chronic liver disease, or the side effects of certain therapeutic medications. The strategy to lower the MCV must align precisely with the underlying biological mechanism.
Targeted Nutritional Adjustments
Nutritional deficiencies are among the most direct and treatable causes of macrocytosis, particularly those involving Vitamin B12 and folate. Vitamin B12, or cobalamin, is essential for the synthesis of DNA and for maintaining nerve health.
To address a Vitamin B12-related elevation, one should focus on increasing intake of animal products such as meat, fish, dairy, and eggs, as B12 is not naturally present in plant foods. Individuals with absorption issues, such as those with pernicious anemia, may require medical intervention like B12 injections or high-dose oral supplements to bypass the gastrointestinal absorption pathway.
Folate, or Vitamin B9, works closely with B12 in DNA production, and a deficiency also leads to macrocytosis. Folate is readily available in foods like leafy green vegetables, citrus fruits, legumes, and fortified grain products. Initiating folate supplementation without first assessing B12 status can mask a B12 deficiency, potentially allowing neurological damage to progress. Supplements should only be used following blood testing to confirm the specific deficiency and ensure appropriate treatment.
Lifestyle and Substance Management
Behavioral and substance-related factors are another common cause of elevated MCV that a person can directly influence through lifestyle changes. Chronic, excessive alcohol consumption is a major contributor to macrocytosis through several mechanisms. Alcohol is directly toxic to the bone marrow, interfering with the normal maturation and division of red blood cell precursors.
It also disrupts the body’s ability to metabolize and absorb folate, exacerbating the deficiency state even with adequate dietary intake. For alcohol-related macrocytosis, the most effective step to lower the MCV is complete abstinence or significant reduction in intake. With cessation, the MCV generally begins to decrease and may take between two to four months to return to the normal reference range as the body produces new, healthy red blood cells.
Certain categories of medications can also cause an elevated MCV by interfering with cell division. Drugs used in chemotherapy, some anti-seizure medications, or antivirals may impair DNA synthesis, mimicking a B12 or folate deficiency. If a medication is suspected, consult a physician to determine if an alternative drug or dosage adjustment is possible. Self-adjusting prescribed medication should not be attempted, as therapeutic benefits must be weighed against the side effect of macrocytosis.
Recognizing Underlying Systemic Conditions
When nutritional and lifestyle adjustments do not resolve an elevated MCV, systemic conditions that require specific medical management must be considered. Chronic liver disease, such as cirrhosis, is a frequent non-nutritional cause of macrocytosis. In this instance, the red blood cell membrane composition is altered due to changes in circulating lipids, resulting in larger cells.
Another endocrine condition that can occasionally lead to macrocytosis is hypothyroidism, where an underactive thyroid gland disrupts the production and maturation of red blood cells in the bone marrow. Addressing the underlying liver or thyroid condition with appropriate medical treatment is the only way to normalize the MCV in these cases.
Persistent or severe macrocytosis may also indicate serious issues involving the bone marrow, such as myelodysplastic syndromes. These conditions are characterized by the ineffective production of blood cells and necessitate consultation with a hematologist for specialized testing and treatment. If the MCV remains high despite addressing diet and substance use, comprehensive medical testing, including liver and thyroid function panels, is necessary to identify and treat the correct underlying condition.