Confused by Your MCV Blood Test? Why Your Cells Are Changing Size + Medically Approved Next Steps

If you've recently had blood work done, you may have noticed a result called MCV on your lab report. Seeing a number that's marked "high" or "low" can feel confusing — especially if you're not sure what it means.

The good news? An abnormal MCV blood test result is common, and in many cases, it's treatable once the cause is identified.

Let's break down what MCV means, why your red blood cells might be changing size, and what medically recommended steps you should take next.

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What Is an MCV Blood Test?

MCV stands for Mean Corpuscular Volume. It measures the average size of your red blood cells.

Red blood cells carry oxygen from your lungs to the rest of your body. Their size matters because it can help doctors understand whether something is affecting your ability to make healthy blood cells.

The MCV blood test is usually part of a Complete Blood Count (CBC) — one of the most common blood tests ordered during routine checkups.

Normal MCV Range

Most laboratories consider a normal MCV to be:

• 80–100 femtoliters (fL) in adults

If your result falls outside this range, your doctor may investigate further.

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What Does It Mean If Your MCV Is High?

A high MCV (over 100 fL) means your red blood cells are larger than normal. This is called macrocytosis.

Common Causes of High MCV

• Vitamin B12 deficiency
• Folate (vitamin B9) deficiency
• Alcohol use
• Liver disease
• Hypothyroidism
• Certain medications (such as chemotherapy drugs or seizure medications)
• Bone marrow disorders (less common, but more serious)

The most common cause worldwide is vitamin deficiency, particularly B12 or folate.

Symptoms You Might Notice

Sometimes there are no symptoms. But if anemia develops, you may experience:

• Fatigue
• Weakness
• Pale skin
• Shortness of breath
• Dizziness
• Tingling or numbness (especially with B12 deficiency)

Because B12 deficiency can affect the nervous system, untreated cases can lead to nerve damage. That's why it's important not to ignore a high MCV blood test result.

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What Does It Mean If Your MCV Is Low?

A low MCV (below 80 fL) means your red blood cells are smaller than normal. This is called microcytosis.

Common Causes of Low MCV

• Iron deficiency anemia (most common cause)
• Chronic blood loss (heavy periods, gastrointestinal bleeding)
• Thalassemia (a genetic blood disorder)
• Chronic disease
• Lead exposure (rare in adults)

Iron deficiency is the leading cause worldwide. It may result from:

• Poor dietary intake
• Pregnancy
• Heavy menstrual bleeding
• Stomach ulcers or colon conditions
• Internal bleeding

Symptoms of Low MCV

Symptoms usually relate to anemia and may include:

• Extreme fatigue
• Shortness of breath
• Cold hands and feet
• Brittle nails
• Headaches
• Cravings for non-food items (like ice or dirt — called pica)

If you're experiencing any combination of these symptoms and want to better understand what might be causing them, Ubie's free AI symptom checker can help you get personalized insights in just a few minutes before your doctor's appointment.

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Can Your MCV Be Normal but You Still Have a Problem?

Yes.

A normal MCV blood test does not always mean everything is fine. Some types of anemia show a normal MCV — this is called normocytic anemia.

Common causes include:

• Chronic kidney disease
• Chronic inflammation
• Early stages of iron deficiency
• Blood loss
• Bone marrow disorders

This is why doctors look at your entire CBC, not just the MCV number.

Other important values include:

• Hemoglobin
• Hematocrit
• RBC count
• RDW (Red Cell Distribution Width)

MCV is one piece of a bigger puzzle.

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Why Do Red Blood Cells Change Size?

Your body constantly produces red blood cells in your bone marrow. To make healthy cells, it needs:

• Iron
• Vitamin B12
• Folate
• Healthy bone marrow function
• Proper hormone balance

If any of these are disrupted, red blood cell production changes — and so does their size.

Think of it like baking. If you're missing key ingredients, the final product won't turn out the same.

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Medically Approved Next Steps After an Abnormal MCV Blood Test

If your MCV is outside the normal range, here's what doctors typically recommend:

1. Repeat Testing (If Needed)

Sometimes abnormal results are temporary or related to mild dehydration or lab variation. Your doctor may recheck levels.

2. Iron Studies

If MCV is low, your doctor may order:

• Ferritin
• Serum iron
• Total iron-binding capacity (TIBC)
• Transferrin saturation

These confirm iron deficiency.

3. Vitamin Testing

If MCV is high, doctors often check:

• Vitamin B12
• Folate
• Methylmalonic acid (in some cases)

4. Thyroid Function Tests

Hypothyroidism can cause macrocytosis.

5. Liver Function Tests

Liver disease can increase red blood cell size.

6. Medication Review

Certain medications affect red blood cell production.

7. Further Evaluation (If Necessary)

If no obvious cause is found, your doctor may refer you to a hematologist for further testing.

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When Is an Abnormal MCV Serious?

Most abnormal MCV blood test results are caused by treatable conditions like nutrient deficiencies.

However, you should seek prompt medical attention if you experience:

• Severe shortness of breath
• Chest pain
• Fainting
• Rapid heart rate
• Neurological symptoms (confusion, difficulty walking, severe numbness)

In rare cases, abnormal MCV may signal:

• Bone marrow disorders (such as myelodysplastic syndrome)
• Severe bleeding
• Advanced liver disease

These conditions require urgent medical evaluation.

If you have concerning symptoms, do not delay — speak to a doctor immediately.

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Can Diet Fix an Abnormal MCV?

Sometimes — but not always.

For Low MCV (Iron Deficiency)

Iron-rich foods include:

• Red meat
• Poultry
• Spinach
• Lentils
• Beans
• Fortified cereals

But dietary changes alone may not correct moderate to severe deficiency. Iron supplements are often needed under medical supervision.

For High MCV (B12 or Folate Deficiency)

Sources include:

• B12: Meat, dairy, eggs
• Folate: Leafy greens, legumes, citrus fruits

Some people (especially vegetarians, vegans, and older adults) may require supplements or injections.

Important: Never start high-dose supplements without medical guidance. Too much iron, for example, can be harmful.

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Key Takeaways About Your MCV Blood Test

• MCV measures the average size of your red blood cells.
• High MCV = large cells (often B12 or folate deficiency).
• Low MCV = small cells (often iron deficiency).
• Most causes are treatable once identified.
• Additional testing is usually needed to find the root cause.
• Serious causes are less common but should not be ignored.

An abnormal MCV blood test result is not a diagnosis by itself. It's a clue.

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What You Should Do Now

1. Review your full lab report — not just MCV.
2. Schedule a conversation with your healthcare provider.
3. Ask what additional testing is needed.
4. Monitor for symptoms like fatigue, dizziness, or weakness.
5. If you're unsure about what your symptoms might mean or want guidance before seeing your doctor, check your symptoms with Ubie's free AI-powered tool to get personalized, immediate insights that can help you prepare for your appointment.

Most importantly, speak to a doctor about any abnormal lab result — especially if you feel unwell. Some causes of abnormal red blood cell size can become serious if left untreated.

The bottom line: An abnormal MCV blood test is common, often manageable, and very treatable once the cause is clear. With the right evaluation and guidance, you can address the issue directly and protect your long-term health.