What Is MCV in a Blood Test? Symptoms and What It Means

MCV stands for Mean Corpuscular Volume, a component of the Complete Blood Count (CBC) test that measures the average size of your red blood cells. Red blood cells (RBCs) are responsible for delivering oxygen throughout your body, and their size can reflect how well they're functioning.

MCV Category	Range (fL)	Notes
Normal	80–100	Typical healthy range
High	>100	May indicate macrocytic anemia
Low	<80	Indicates microcytic anemia

The test doesn't diagnose disease on its own, but it helps providers identify patterns that may suggest vitamin deficiencies, chronic illness, or bone marrow issues.^[1]

If your MCV is above 100 fL, this is referred to as macrocytosis, a condition in which red blood cells are larger than normal. Large RBCs may not function efficiently, and macrocytosis can be a sign of underlying nutritional deficiencies, alcohol use, or chronic health conditions.[2]

Notably, MCV may be elevated even when a person is asymptomatic. That's why identifying the root cause is critical, especially if other values in your CBC are also abnormal.

Symptoms of High MCV

High MCV itself doesn't directly cause symptoms, but the conditions that lead to macrocytosis often do. Depending on the underlying cause, symptoms may include[1,3]:

• Fatigue or weakness
• Pale or yellow-tinted skin
• Shortness of breath
• Tingling or numbness in the hands and feet (commonly seen in B12 deficiency)
• Irritability or difficulty concentrating
• Glossitis (smooth or swollen tongue)

If these symptoms are present alongside high MCV levels, your healthcare provider may order further tests to pinpoint the cause.

Causes of High MCV

There are many possible causes of macrocytosis, but some are much more common than others. Let's explore the most frequent triggers[3]:

• Vitamin B12 Deficiency: B12 is essential for the formation of red blood cells and neurological function. When B12 levels are low, it impairs DNA synthesis in developing RBCs, leading to larger but less functional cells.
• Folate Deficiency: Folate (vitamin B9) works closely with B12 in RBC production. Inadequate folate, often due to poor diet, alcohol use, or malabsorption, can result in macrocytic anemia.
• Chronic Alcohol Use: Alcohol has a toxic effect on bone marrow and can impair the absorption of folate and B12, both of which contribute to larger RBCs.
• Liver Disease: Liver dysfunction is associated with altered lipid metabolism, which can change the shape and size of red blood cells, raising MCV levels.
• Myelodysplastic Syndromes (MDS): These are a group of bone marrow disorders more commonly found in older adults. They often cause abnormal blood cell development, including macrocytosis.[4]
• Certain Medications: Some medications may interfere with DNA synthesis or nutrient absorption, contributing to macrocytosis. These include[3]:
  • Chemotherapy drugs
  • Anti-seizure medications (e.g., phenytoin, valproic acid)
  • Methotrexate
  • Sulfasalazine
• Smoking and COPD: Smoking and chronic lung disease can lead to compensatory increases in red blood cell production, which may affect MCV values.
• Hypothyroidism: An underactive thyroid can slow many bodily functions, including red blood cell production, and may cause macrocytosis.[3]

Testing note: Because an underactive thyroid can contribute to elevated MCV, thyroid testing may be appropriate—especially if you’re experiencing fatigue, cold sensitivity, or brain fog.

Check your thyroid markers with Everlywell’s Thyroid Test.

What to Eat to Help Lower MCV

Category	Foods / Recommendations
Vitamin B12-Rich Foods [6]	Eggs; dairy (yogurt, cheese, milk); fish (salmon, tuna); red meat; fortified cereals or plant-based milk
Folate-Rich Foods [7]	Spinach; kale; avocados; lentils; beans; oranges
Lifestyle Tips	Avoid excessive alcohol; maintain a balanced, nutrient-rich diet

If your MCV is below 80 fL, this is referred to as microcytosis—a condition in which red blood cells are smaller than normal. Smaller RBCs may carry less oxygen throughout the body, which can affect energy levels and overall function. Low MCV is often associated with anemia or conditions that impact hemoglobin production.[2]

In some cases, low MCV may be identified before symptoms appear. That’s why it’s important to evaluate the underlying cause—especially if other values in your complete blood count (CBC) are outside the normal range.

Symptoms of Low MCV

Low MCV itself does not directly cause symptoms, but the conditions behind it often do. Depending on the cause, symptoms may include:

• Fatigue or low energy
• Pale skin
• Weakness
• Difficulty concentrating
• Shortness of breath
• Headaches

If these symptoms occur alongside low MCV levels, further testing may be needed to determine the root cause.

Causes of Low MCV

There are several potential causes of microcytosis, with some being more common than others. These include:

• Iron Deficiency Anemia: The most common cause of low MCV. It occurs when the body doesn’t have enough iron to produce healthy hemoglobin, often due to poor diet, blood loss, or chronic illness.
• Thalassemia: A genetic blood disorder that affects hemoglobin production, leading to smaller, less effective red blood cells.
• Anemia of Chronic Disease: Long-term health conditions can interfere with how the body uses iron and produces red blood cells.
• Sideroblastic Anemia: A condition in which the body cannot properly incorporate iron into hemoglobin, even when iron levels are adequate.
• Lead Exposure: In rare cases, lead toxicity can interfere with red blood cell production and result in smaller RBCs.

If your MCV levels are outside the normal range—whether high or low—it’s a good idea to speak with a healthcare provider, especially if you’re experiencing symptoms like fatigue, weakness, shortness of breath, or changes in skin tone.

Abnormal MCV levels can be an early indicator of underlying conditions, even if you don’t have noticeable symptoms. A healthcare provider can help determine the cause and whether further evaluation is needed.

Depending on your results, follow-up testing may include [4]:

• Vitamin B12 and folate levels
• Iron studies or ferritin levels
• Liver function tests
• Thyroid panel
• Reticulocyte count
• Peripheral blood smear

Early evaluation can help identify the root cause and guide appropriate treatment, if needed.

Because a high MCV can reflect vitamin deficiencies, liver health, thyroid function, or broader metabolic patterns, the most helpful next step is often to look at your health in context—not in isolation.

Everlywell 360 measures 80+ biomarkers to help you understand what may be contributing to elevated MCV and what to discuss with your provider next.

If hypothyroidism is a possibility—especially with fatigue, cold sensitivity, or brain fog—you may also consider the Everlywell Thyroid Test as a targeted follow-up.

As always, be sure to review your results with a healthcare provider, who can help interpret them in the context of your overall health and guide next steps.