Mean Corpuscular Volume (MCV) is a routine measurement in a complete blood count (CBC) test. It indicates the average size of red blood cells, which transport oxygen throughout the body. Evaluating MCV is a standard part of health assessments, helping identify potential red blood cell issues.
What is MCV?
Mean Corpuscular Volume (MCV) quantifies the average size of red blood cells in a blood sample. This measurement is part of a complete blood count (CBC), a common test used to assess overall health. Red blood cells carry oxygen from the lungs to every cell in the body.
A low MCV result, known as microcytosis, indicates red blood cells are smaller than typical. For adults, the normal MCV range is 80 to 100 femtoliters (fL). An MCV reading below 80 fL suggests smaller-than-average red blood cells, which can signal various underlying health conditions.
Primary Causes of Low MCV
Low MCV is associated with conditions causing smaller red blood cells. The most common cause is iron deficiency anemia. Iron is essential for hemoglobin production, the protein in red blood cells that binds oxygen. Insufficient iron leads to smaller red blood cells with reduced oxygen-carrying capacity. This deficiency can stem from inadequate dietary intake, poor absorption, or chronic blood loss, such as from heavy menstrual periods or gastrointestinal bleeding.
Another cause of low MCV is thalassemia, a group of inherited blood disorders. Thalassemia involves abnormal hemoglobin production, impacting red blood cell formation and causing them to be smaller. Individuals with a thalassemia trait often have smaller red blood cells and may experience mild or no symptoms. This condition is distinct from iron deficiency and does not require iron supplementation.
Anemia of chronic disease (ACD) can also result in low MCV. This anemia occurs with ongoing inflammatory conditions, chronic infections, or certain systemic illnesses. In ACD, the body’s ability to utilize iron is impaired, even with adequate iron stores, leading to smaller red blood cells. Less common causes include lead poisoning, which interferes with heme synthesis.
Exploring the Cancer Connection
While a low MCV is not a direct diagnostic marker for cancer, it is often linked to more common conditions like iron deficiency or thalassemia. However, certain cancers can indirectly contribute to a low MCV.
One way cancer can lead to low MCV is through chronic blood loss, resulting in iron deficiency anemia. Gastrointestinal cancers, such as colon cancer, can cause slow, persistent bleeding that gradually depletes the body’s iron stores. This leads to the production of smaller, iron-deficient red blood cells.
Additionally, some cancers can induce chronic inflammation. This inflammation can contribute to anemia of chronic disease, which may present with a low MCV. In these cases, cancer triggers systemic processes that impair iron utilization or red blood cell production. Low MCV observed in individuals with cancer is typically a secondary effect, not a primary indicator of malignancy.
Next Steps After a Low MCV Result
A low MCV result warrants consultation with a healthcare professional to determine the underlying cause. An MCV value alone cannot diagnose a specific disease, but it serves as an important clue that guides further medical investigation. The doctor will consider the MCV result alongside other parameters from your complete blood count and your medical history.
Common follow-up tests include iron studies, which measure various iron levels in the blood, such as serum iron, ferritin, and transferrin saturation, to assess for iron deficiency. If thalassemia is suspected, especially based on ethnic background or family history, a hemoglobin electrophoresis might be performed to analyze the types and amounts of hemoglobin present. A peripheral blood smear, examining blood cells under a microscope, can provide additional morphological details. A low MCV is a finding that requires medical evaluation, but it is frequently due to treatable and non-serious conditions.