Writer: Jillian Foglesong Stabile, MD, FAAFP, DABOM
If you've recently had a blood test and saw that your MCV is high, you might be wondering what that means—and whether you should be concerned. MCV, or Mean Corpuscular Volume, measures the average size of your red blood cells. When this number is elevated, it can signal changes in your body's nutrient levels, liver function, or bone marrow activity. This guide will review everything you need to know about a high MCV.
What Is MCV in a Blood Test?
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.
- Normal MCV range: typically between 80 and 100 femtoliters (fL)
- High MCV: above 100 fL
- Low MCV: below 80 fL (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]
What Is Considered a High MCV?
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.
What Causes a 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]:
1. 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.
2. 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.
3. 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.
4. Liver Disease
Liver dysfunction is associated with altered lipid metabolism, which can change the shape and size of red blood cells, raising MCV levels.
5. 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]
6. 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
7. 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 →
8. Smoking and COPD
Smoking and chronic lung disease can lead to compensatory increases in red blood cell production, which may affect MCV values.
Looking for a more complete picture? A high MCV can reflect vitamin deficiencies, liver health, thyroid function, or broader metabolic patterns—not just a single lab value.
Everlywell 360 helps you look beyond MCV alone by measuring 80+ biomarkers that provide a more complete view of your health.
Can High MCV Be a Sign of Cancer?
This is a common concern. While macrocytosis is not a direct sign of cancer, it may appear in people undergoing chemotherapy or those with myelodysplastic syndromes, a precursor condition to leukemia.
However, in most people, high MCV is due to nutrient deficiency or lifestyle factors, not cancer. If cancer is suspected, your provider will typically look for additional symptoms and abnormal lab values before ordering further tests.[4]
What Drugs Can Cause High MCV?
Some medications are known to elevate MCV as a side effect, particularly those that impact folate metabolism or bone marrow function [4]:
- Methotrexate
- Antiretrovirals (e.g., zidovudine)
- Chemotherapy agents
- Antiepileptic drugs (e.g., phenytoin)
If you're taking these medications, your provider may monitor your bloodwork regularly.
How Is High MCV Treated?
Treatment depends entirely on the underlying cause. In most cases, macrocytosis is reversible with appropriate intervention. [5]
If due to B12 or folate deficiency:
- Oral or injectable vitamin B12
- Folic acid supplementation
- Diet changes to include leafy greens, legumes, citrus fruits, dairy, and eggs
If due to alcohol use:
- Reduce or eliminate alcohol
- Address any nutritional deficiencies
- Monitor liver function
If medication-induced:
- Adjusting or switching medications (only under provider guidance)
If due to chronic disease:
- Treat the root condition (e.g., thyroid disease, liver disease, MDS)
Can Dehydration Affect MCV?
Not directly. Dehydration can affect hematocrit and hemoglobin concentration, but MCV reflects red blood cell size, not fluid volume. However, severe dehydration could potentially skew test interpretation if other values are also altered.
What to Eat to Help Lower MCV
If your MCV is high due to vitamin deficiency, incorporating the following foods may help normalize levels:
Foods high in vitamin B12 [6]:
- Eggs
- Dairy (yogurt, cheese, milk)
- Fish (salmon, tuna)
- Red meat
- Fortified cereals or plant-based milk
Foods high in folate [7]:
- Spinach
- Kale
- Avocados
- Lentils
- Beans
- Oranges
Avoid excessive alcohol and ensure a well-rounded, nutrient-rich diet.
How Much Alcohol Raises MCV?
Chronic alcohol use, even at moderate levels, can increase MCV by damaging bone marrow and depleting folate stores. Some studies show changes in MCV can occur with as few as 3–4 drinks per day over several weeks.[8] However, effects vary based on individual metabolism, diet, and overall health.
When Should You See a Healthcare Provider?
If your MCV is high, speak with your healthcare provider, especially if you're also experiencing symptoms like fatigue, numbness, or pale skin. Your healthcare provider may order follow-up tests, such as [4]:
- Vitamin B12 and folate levels
- Liver function tests
- Thyroid panel
- Reticulocyte count
- Peripheral blood smear
Need help connecting the dots? If your Everlywell 360 results raise questions related to elevated MCV or related markers, you can follow up with a clinician to review your results and discuss appropriate next steps.
In rare cases, a bone marrow biopsy may be necessary to rule out more serious conditions.
Conclusion
A high MCV blood test result can be a valuable early warning sign that your body isn't getting the nutrients it needs—or that a deeper issue needs attention. Whether the cause is as simple as a vitamin deficiency or linked to a chronic condition, high MCV is often manageable and treatable when addressed early.
By understanding your MCV levels, tracking your symptoms, and following up with the right tests, you can take meaningful steps toward restoring balance in your health.
Take Control of Your Health With Everlywell
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.
If your results raise questions, you can also follow up with a virtual visit to review your results and discuss appropriate next steps with a licensed clinician.