Mean Corpuscular Volume (MCV) is a measurement that indicates the average size of red blood cells in a blood sample. When MCV results are high, it means that the red blood cells are larger than their typical size, a condition medically referred to as macrocytosis. This finding is a laboratory indicator that prompts further investigation into its underlying cause.
Understanding MCV Results
MCV quantifies the average volume of individual red blood cells, with results commonly expressed in femtoliters (fL). For most adults, a typical MCV reference range falls between 80 and 100 fL. An MCV value consistently above this range, usually over 100 fL, indicates that the red blood cells circulating in the bloodstream are larger than normal. This elevated MCV is not a diagnosis, but a clue signaling a need for further medical evaluation.
Common Causes of Elevated MCV
Several factors can lead to an elevated MCV, each impacting red blood cell development and size. A frequent cause is vitamin B12 deficiency, crucial for DNA synthesis in red blood cell precursors. Without enough B12, these cells grow larger but don’t divide properly, leading to macrocytic anemia. Similarly, folate deficiency impedes red blood cell maturation, as folate also plays a direct role in DNA synthesis and cell division.
Excessive alcohol consumption can directly suppress bone marrow activity and interfere with red blood cell production, resulting in larger red blood cells. Chronic liver disease can impair the liver’s ability to metabolize certain substances, leading to changes in red blood cell membranes causing them to swell. An underactive thyroid gland, known as hypothyroidism, can be associated with macrocytosis.
Certain medications, such as certain chemotherapy or antiviral drugs, can interfere with DNA synthesis or red blood cell maturation, increasing MCV. Reticulocytosis, an increase in immature red blood cells (reticulocytes), can also transiently elevate MCV. Reticulocytes are larger than mature red blood cells and are released from the bone marrow in response to increased red blood cell destruction or loss. More serious causes include bone marrow disorders like Myelodysplastic Syndromes (MDS), which involve abnormal production of blood cells, including large, dysfunctional red blood cells.
Recognizing Associated Symptoms
While an elevated MCV itself does not cause symptoms, the underlying conditions responsible for macrocytosis manifest with various signs. Individuals might experience generalized fatigue and weakness, common indicators of anemia. Shortness of breath, during physical exertion, can also occur due to the reduced oxygen-carrying capacity of the blood.
Pale skin is a visual cue, resulting from a decrease in healthy red blood cells. For specific deficiencies like vitamin B12, neurological symptoms like numbness or tingling in the hands and feet might develop. These symptoms can range in severity and vary widely depending on the specific cause of the high MCV.
Next Steps After a High MCV Result
Upon receiving a high MCV result, a healthcare provider will initiate further diagnostic steps to pinpoint the underlying cause. This involves additional blood tests, including vitamin B12 and folate levels, liver function, and thyroid hormone levels. A peripheral blood smear may also be examined to observe red blood cells directly and identify abnormalities.
A comprehensive medical history, including dietary habits, alcohol intake, and current medications, along with a physical examination, provides valuable context. Treatment for an elevated MCV addresses the root cause identified through these investigations, not the MCV value itself. This could involve dietary changes, vitamin supplements for nutritional deficiencies, adjusting contributing medications, or managing chronic conditions like liver disease or hypothyroidism. Medical evaluation after a high MCV result is important for understanding and resolving the underlying health concern.