Mean Corpuscular Volume (MCV) is a component of a routine complete blood count (CBC) that provides insight into the average size of your red blood cells. When this value is elevated, it indicates that your red blood cells are larger than typical, a condition known as macrocytosis. It indicates various underlying health conditions, prompting further investigation.
What MCV Measures
Red blood cells transport oxygen throughout the body. The MCV test is a standard part of a complete blood count (CBC).
A normal MCV value for adults falls within a range of 80 to 100 femtoliters (fL). An MCV exceeding 100 fL indicates larger red blood cells. While a high MCV does not by itself diagnose a specific medical condition, it points to a potential issue with red blood cell production or maturation that requires additional medical assessment.
Primary Causes of Elevated MCV
An elevated Mean Corpuscular Volume can stem from several factors, each impacting red blood cell development differently. Understanding these causes helps narrow down the reasons for larger red blood cells.
Nutritional deficiencies are a cause of macrocytosis, particularly a lack of vitamin B12 or folate (vitamin B9). Both vitamins are important for DNA synthesis within developing red blood cells in the bone marrow. When these nutrients are insufficient, red blood cells cannot divide properly, leading to the production of fewer but abnormally large and immature cells. Pernicious anemia, an autoimmune condition preventing B12 absorption, is an example of how B12 deficiency can lead to elevated MCV.
Chronic alcohol consumption can lead to an elevated MCV. Alcohol has a direct toxic effect on the bone marrow, impairing its ability to produce healthy red blood cells. Additionally, excessive alcohol intake can interfere with the absorption and metabolism of essential nutrients like folate, further contributing to the production of larger red blood cells. Macrocytosis in liver disease, even when not alcohol-related, can occur due to changes in lipid metabolism that alter the red blood cell membrane, increasing its surface area and size.
An underactive thyroid gland, a condition known as hypothyroidism, can be associated with macrocytosis. The exact mechanism is not fully understood, but it is believed to affect red blood cell production or maturation processes. Certain medications can also induce an elevated MCV as a side effect. These include some chemotherapy drugs, antiretroviral medications used in HIV treatment, and certain anticonvulsants, often by interfering with DNA synthesis or folate metabolism.
Less commonly, bone marrow disorders such as myelodysplastic syndromes (MDS) can manifest with a high MCV. MDS are a group of conditions where the bone marrow produces dysfunctional and immature blood cells, often leading to macrocytic anemia due to ineffective red blood cell production. While less frequent than nutritional deficiencies or alcohol use, MDS represents a more serious underlying cause.
Associated Symptoms and Further Evaluation
A high MCV reading itself does not cause noticeable symptoms; rather, any symptoms experienced are a result of the underlying condition responsible for the elevated red blood cell size. Common symptoms that might prompt further medical attention include persistent fatigue, general weakness, and pale skin, which are often indicative of anemia. Individuals might also experience shortness of breath, dizziness, or lightheadedness due to reduced oxygen delivery to tissues.
Specific underlying causes can present with additional symptoms. For instance, vitamin B12 deficiency may lead to neurological symptoms such as tingling or numbness in the hands and feet, or difficulty concentrating. Liver disease might present with jaundice, a yellowing of the skin or eyes. Digestive issues like diarrhea can also be associated with conditions causing elevated MCV.
Upon discovering an elevated MCV, a healthcare professional will conduct a thorough medical history and physical examination. Further evaluation often involves additional blood tests to pinpoint the specific cause. These may include measuring levels of vitamin B12 and folate, assessing liver function through liver enzyme tests, and checking thyroid stimulating hormone (TSH) levels.
A reticulocyte count, which measures immature red blood cells, and a peripheral blood smear, which allows for microscopic examination of red blood cell shape and size, can provide further clues. Lifestyle factors, such as alcohol consumption and dietary habits, are also considered in the diagnostic process. Consulting a healthcare professional for proper diagnosis and management is important, as self-diagnosis based solely on a high MCV value is not appropriate.