An elevated Mean Corpuscular Volume (MCV) is a measurement included in a standard Complete Blood Count (CBC). While a high MCV value indicates a change in red blood cell production, this result is only a single piece of information. This finding is common and often points toward manageable causes related to nutrition or lifestyle.
What High MCV Means
The MCV measures the average volume, or size, of your red blood cells. Red blood cells transport oxygen throughout the body, and their size can impact this function. For most adults, a normal MCV value falls within a range of 80 to 100 femtoliters (fL).
An MCV result above 100 fL is termed macrocytosis, meaning the red blood cells are larger than average. This increase in size happens when the cells fail to divide properly during formation in the bone marrow. The presence of these oversized cells indicates an underlying issue affecting cell development. Evaluating this measurement alongside other blood counts helps determine the cause of the enlargement.
Nutritional and Lifestyle Factors
The most frequent reasons for an elevated MCV relate to deficiencies in specific B vitamins and long-term lifestyle habits. Vitamin B12 and folate (Vitamin B9) are cofactors in the production of DNA within red blood cell precursors. A deficiency in either vitamin impairs DNA synthesis, preventing the cell from completing its division.
This failure results in the release of fewer, but larger, immature red blood cells, which drives the MCV value up. B12 deficiency can be caused by low dietary intake, particularly in vegan or vegetarian diets, or by absorption issues like pernicious anemia. Folate deficiency is linked to poor absorption or inadequate intake of fruits and vegetables.
Chronic alcohol consumption is another cause of macrocytosis. Alcohol has a direct toxic effect on the bone marrow, interfering with the maturation process of red blood cells. It can also impair the absorption of essential nutrients like folate. In many cases, the MCV begins to normalize within a few months of alcohol cessation.
Systemic Disease Indicators
While nutritional and lifestyle factors are the most common causes, an elevated MCV can point to systemic health issues. Chronic liver disease, regardless of the cause, frequently leads to macrocytosis. Liver dysfunction affects lipid metabolism, which changes the red blood cell membrane composition, causing the cell to swell.
An underactive thyroid, known as hypothyroidism, is also associated with an increased MCV. The slowed metabolism affects the bone marrow environment and red blood cell production. Furthermore, certain medications can cause macrocytosis as a side effect, including chemotherapy agents, antiretroviral drugs, and anticonvulsants.
In rare instances, a high MCV may signal a primary bone marrow disorder, such as Myelodysplastic Syndrome (MDS). These conditions involve the abnormal production of blood cells within the bone marrow. If MDS is suspected, the elevated MCV is typically accompanied by abnormalities in other blood cell lines, such as low white blood cell or platelet counts.
Consulting Your Doctor
An elevated MCV reading warrants a conversation with your healthcare provider for further investigation. The initial step involves a detailed review of your medical history, diet, medication use, and alcohol intake, as these provide immediate clues to the cause. Your doctor will likely order follow-up blood work to pinpoint the issue.
Subsequent testing often includes specific measurements of serum Vitamin B12 and folate levels to confirm or rule out a deficiency. Liver function tests may also be ordered to assess liver health. In some cases, a peripheral blood smear is examined under a microscope to inspect the shape and characteristics of the red blood cells. The MCV is one data point, and a full picture of your health requires this comprehensive diagnostic process.