A Mean Corpuscular Volume (MCV) result is one component of a standard complete blood count (CBC), a common blood test used to evaluate overall health. This measurement provides a value for the average size of your red blood cells, which are responsible for transporting oxygen from the lungs to all tissues. The physical characteristics of these cells, including their volume, offer information about their ability to perform this function.
Understanding Your MCV Result
The result of an MCV test is measured in a unit called femtoliters (fL), and the reference range for most adults is between 80 and 100 fL. A value of 100 fL places your red blood cells at the very top of this standard range. Depending on the specific laboratory, this result may be considered the upper limit of normal or slightly elevated.
When MCV levels are consistently above 100 fL, the medical term used to describe the presence of abnormally large red blood cells is macrocytosis. This finding is not a disease itself but indicates that the red blood cells are larger than average. An MCV of 100 fL signals that a closer look at the factors influencing red blood cell development is warranted.
Potential Causes of an Elevated MCV
One of the most frequent reasons for an elevated MCV is a deficiency in certain vitamins. Other causes range from lifestyle factors to underlying medical conditions.
- Vitamin B12 or Folate Deficiency: These vitamins are necessary for the synthesis of DNA within developing red blood cells in the bone marrow. When these nutrients are lacking, cell division is impaired, leading to the production of large, immature red blood cells called megaloblasts. This condition is a specific type of macrocytosis known as megaloblastic anemia.
- Alcohol Consumption: Chronic and heavy alcohol consumption can exert a toxic effect on the bone marrow, disrupting normal red blood cell development. It also interferes with the body’s ability to properly absorb and utilize essential nutrients, particularly folate.
- Liver Disease: Liver disease, whether related to alcohol or other causes, can alter the lipid composition of the red blood cell membrane. This leads to an increased deposition of cholesterol and phospholipids on the cell surface, causing them to become larger.
- Hypothyroidism: An underactive thyroid gland can be associated with macrocytosis. Thyroid hormones influence the production of red blood cell precursors, and insufficient hormone levels can dampen this process, resulting in an increased MCV.
- Medications: Certain drugs that interfere with DNA synthesis, such as chemotherapy agents like methotrexate or some anticonvulsant medications, can cause macrocytosis. These substances can directly impact bone marrow function or interfere with vitamin metabolic pathways.
Associated Signs and Symptoms
Many people with an elevated MCV, particularly when it is only slightly high, may not experience any noticeable symptoms. When symptoms do appear, they are often related to the onset of anemia, which is a reduced number of red blood cells. General symptoms of anemia include persistent fatigue, weakness, shortness of breath during physical activity, and pale skin.
Specific underlying causes of macrocytosis can produce more distinct symptoms. A deficiency in vitamin B12, for example, can cause neurological issues such as tingling or numbness in the hands and feet, difficulty with balance, or memory problems. Another sign of B12 or folate deficiency can be glossitis, which is a sore, smooth, and reddened tongue.
Symptoms may also point toward other potential causes. If liver disease is the root issue, a person might experience jaundice, a yellowing of the skin and eyes. When hypothyroidism is the cause, individuals might report fatigue, sensitivity to cold, and unexplained weight gain.
Next Steps and Diagnostic Process
An MCV of 100 fL is a laboratory finding, not a final diagnosis. It prompts your healthcare provider to investigate further to determine the underlying cause, placing the result in the context of your overall health and medical history.
To identify the reason for the enlarged red blood cells, a provider will order a panel of follow-up blood tests. This investigation begins with measuring the levels of vitamin B12 and folate in the blood. Liver function tests and a thyroid panel are also common to assess for liver or thyroid conditions.
A peripheral blood smear is also part of the diagnostic process. For this test, a drop of blood is examined under a microscope, allowing for a direct visual inspection of the blood cells. A technician looks for abnormalities in cell shape, such as round macrocytes that can suggest liver disease or macro-ovalocytes that suggest a B12 or folate deficiency. A reticulocyte count may also be performed to measure the bone marrow’s production of new red blood cells.