MCV Blood Test High: 9 Serious Causes You Shouldn’t Ignore

Many patients are surprised when their blood test results show MCV blood test high. A high MCV does not directly indicate any diagnosis, it is just more of a diagnostic clue.

In this guide I will explain, what MCV blood test high means, what its clinical significance is based on my experience and peer-reviewed resources.

What is MCV?

MCV (Mean Corpuscular Volume) measures the average size of your red blood cells. It is one part of the complete blood count (CBC) and the basic blood count (BBC) which are used to assess blood health.

A normal MCV is 80–100 femtolitres (fL) [1]. When your results show MCV blood test high, it means your red blood cells are larger than normal — a condition called macrocytosis [2].

Macrocytosis is not always pathological, but some vitamin deficiencies, heavy alcohol consumption, and certain bone marrow diseases may cause macrocytosis.

Why Does MCV Blood Test High Matter?

Red blood cells carry oxygen to the tissues. Red blood cells that are too large or irregularly shaped carry oxygen less well due to the longer diffusion distance.

We doctors treat MCV blood test high as an early warning sign. It’s not specific to any disease and it doesn’t directly diagnose anything, but it prompts further testing [3].

Typically, a high MCV is associated with a deficiency in vitamin B12 or folate. Other causes of high MCV include alcohol intake, liver or thyroid disorders, certain medications, or bone marrow conditions [3,4].

What Counts as “High MCV”?

Although laboratory reference ranges vary slightly, typical cutoffs are:

• 80–100 fL: is considered “normal”. These reference value limits are defined so that 95% of the population falls within this range.
• >100 fL: is considered macrocytosis or “high MCV”
• >115 fL: typically called severe macrocytosis, which is often associated with vitamin deficiency or severe bone marrow changes [1,3]

Mild macrocytosis often does not require special measures, but monitoring and control tests are recommended,

It is important to be aware that a mixed situation, where, for example, a simultaneous deficiency of iron and vitamin B12 and/or folate can have opposite effects and mask the MCV value, making it appear normal.

Common Causes of MCV Blood Test High

Macrocytosis can be divided into megaloblastic and non-megaloblastic:

• Megaloblastic macrocytosis is caused by disruption of DNA synthesis. Common causes include vitamin B12 and folate deficiency.
• Non-megaloblastic macrocytosis is due to causes other than disruption of DNA synthesis. Common causes include alcohol use, liver disease, hypothyroidism, certain medications, bone marrow disorders, reticulocytosis.

1. Vitamin B12 Deficiency

In clinical situations, I often encounter megaloblastic anemia, which is caused by vitamin B12 deficiency. This is also, according to research, the most common cause for a MCV blood test high [5].

Vitamin B12 is required for DNA synthesis and red blood cell formation. When DNA synthesis is disrupted, cell division slows down, although hemoglobin production continues. In this case, the dividing cells become larger and contain more hemoglobin.

Common causes:

• Vegan-focused diet without supplements
• Pernicious anemia i.e. a condition in which vitamin B12 is not absorbed due to a deficiency of intrinsic factor
• Long-term use of metformin or acid-reducing medications [5].

I occasionally see patients who follow a completely vegan diet. In my experience, they are often aware of the lack of vitamin B12 in a vegan diet, so they often know how to compensate for their diet. On the other hand, pernicious anemia has often come as a surprise to my patients, which often leads to further tests, and megaloblastic anemia may reveal a vitamin B12 deficiency.

2. Folate (Vitamin B₉) Deficiency

Folate deficiency also interferes with DNA synthesis, which can also cause macrocytosis, which shows up in as a high MCV blood test.

Causes:

• Lack of vegetables in the diet
• Medications
• Excessive alcohol consumption
• Rapid cell turnover (such as pregnancy, hemolysis, chronic bleeding, lactation, inflammation, malignancies)
• Malabsorption (e.g., celiac disease, Crohn’s disease) [7]

It is important to remember that B12 and folate deficiency may occur simultaneously. Therefore, it is important to make an accurate differential diagnosis before replacement therapy.

In my work, I encounter patients whose risk of folate deficiency is increased by methotrexate medication and other cytostatic drugs, which are often used to treat severe autoimmune diseases such as rheumatoid arthritis. Rheumatologists in Finland, however, most often know to routinely start patients on folate supplements, which reduces the risk.

3. Alcohol Use

Alcohol causes macrocytosis through several mechanisms. First, alcohol is a bone marrow toxin, and second, it disrupts cell membranes [8,9].

MCV elevation has been used clinically as an indirect crude measure of alcohol consumption, although CDT (Carbohydrate-Deficient Transferrin), GT (Gamma-glutamyltransferase) and PEth (Phosphatidylethanol) are now more commonly used due to their sensitivity.

After abstinence, the high MCV blood test typically normalizes within 2–4 months, although liver values return more quickly.

From time to time, a patient’s alcohol use comes up during routine examinations, such as driver’s license checks or periodic occupational health checks. Understandably, my patients who consume alcohol do not always want to be tested for alcohol-specific tests, such as CDT and PEth, so often a high MCV is precisely what raises suspicion. As mentioned at the beginning, MCV is often more of a diagnostic clue than a test that reveals the diagnosis.

4. Liver Disease

Fatty liver, hepatitis, or cirrhosis can alter the red cell membrane, producing MCV blood test high values, as excess lipids accumulate on the surface of red blood cells, increasing the cell surface area without increasing the amount of hemoglobin [10].

Fatty liver is a fairly common finding in my practice, and during regular check-ups for many of my patients, the condition is usually revealed by the patient’s slightly elevated liver values. In my patients, these are often dietary in origin, where the patient’s diet is too animal-based.

5. Hypothyroidism

Hypothyroidism suppresses bone marrow function, which slows down erythropoiesis. Cells divide more slowly, giving them more time to grow, which may lead to MCV blood test high [11].

Hypothyroidism is a common underlying condition in my patients. They are often identified by the thyroxine medication on the medication list. Often, a high MCV also corrects after starting thyroxine if the macrocytosis is due to hypothyroidism alone.

6. Medications

Some drugs directly slow down red blood cell DNA synthesis or directly affect the bone marrow, such as chemotherapy, some anticonvulsants and some antiretrovirals [12,3]. You should consult your doctor about your medications if your MCV blood test high persists.

Some of my patients who receive certain cytostatics also receive folate supplements, as some of these drugs interfere with DNA synthesis. DNA synthesis interference can also manifest as macrocytosis and an increase in MCV.

7. Bone Marrow Disorders

Especially in elderly patients, macrocytosis can signal myelodysplastic syndromes (MDS), which affect blood cell production [13]. These typically require comprehensive care from a hematologist.

In my practice, I have mainly only encountered myelodysplastic syndromes in the elderly, as they are rare in young patients.

8. Reticulocytosis

In anemia and hemolysis, the bone marrow produces more new red blood cells, which is seen as reticulocytosis. Reticulocytes are larger than old red blood cells and thus can temporarily make MCV blood test high [3].

I have occasionally encountered reticulocytosis in bleeding patients. Most often, the chronic bleeding in patients is due to gastrointestinal bleeding, although sometimes heavy menstruation can cause reticulocytosis in some patients.

How Doctors Evaluate MCV Blood Test High

Evaluation usually includes:

1. Full blood count (for anemia pattern and RDW)
2. Vitamin B₁₂ and folate levels
3. Liver enzymes and thyroid tests
4. Alcohol and medication review
5. Peripheral smear examination (oval macrocytes vs. round macrocytes)
6. Bone marrow studies if malignancy or MDS is suspected [3,13]

However, it is good to note that a large number of my patients who consume a lot of alcohol usually downplay their alcohol use, so it is usually worth asking the anamnesis carefully in this regard.

Symptoms Associated with MCV Blood Test High

You may have no symptoms at all, or you might notice signs from the underlying cause:

• Fatigue or weakness
• Tingling or numbness (B12)
• Jaundice/Icterus or abdominal fullness (liver)
• Weight gain or sluggishness (thyroid)
• Cognitive or mood changes

Every now and then I encounter patients with jaundice. I usually refer them to the hospital for acute evaluation, because unfortunately, the cause has often been malignancy, cholestasis or acute hepatitis, which may require hospital assessment.

What To Do If You Have MCV Blood Test High

• Usually there’s no need to panic: mild elevations are common.
• Improve diet: increase foods rich in B₁₂ (meat, eggs, fish) and folate (leafy greens, legumes).
• Reduce alcohol intake.
• Review medications with your doctor.
• Re-test after 6–12 weeks or sooner if symptoms persist.

In practice, I usually arrange repeat laboratory testing after 1–2 months if there is no history of alcohol use, a special diet, a history of bleeding, or any other clear explanatory factor. Fortunately, it is often just a harmless side effect.

Is It Dangerous?

MCV blood test high itself isn’t harmful — the cause might be. Fortunately though, most of the time, a single high MCV value in my patients does not lead to any serious diagnoses.

Nutritional deficiencies and thyroid or liver problems are treatable. Unaddressed B12 deficiency or marrow disorders require more urgent attention. In addition, the instructions are clear for alcohol users.

How to Lower MCV Blood Test High

Underlying Cause	Treatment
Vitamin B₁₂ deficiency	Oral or injectable B₁₂ therapy
Folate deficiency	Dietary folate or supplements
Alcohol-related	Abstinence or reduction
Hypothyroidism	Thyroxine replacement
Drug-induced	Dose review or substitution
Liver disease	Treat underlying cause

MCV usually returns to normal within 1–4 months once the cause is corrected.

Prognosis

Most cases of MCV blood test high are reversible. From my experience, nutritional and alcohol-related causes typically resolve quickly, while chronic diseases may take longer. Early diagnosis of MDS improves long-term outcomes [13].

Unfortunately, many of my patients downplay their alcohol consumption and are often not ready to give up alcohol, while changes in diet are often easier to implement.

How MCV Relates to Other Blood Tests

A high MCV is often an incidental finding. In practice, MCV is very rarely measured in isolation and it is almost always a part of a baic blood count (BBC) and complete blood count (CBC), in which other blood cell-related parameters are routinely measured.

In practice, I almost always order a blood count from patients when they have any lab tests. The blood count includes several key markers that work together to give a full picture of your red cell and platelet health. When your MCV blood test high result appears, it often helps to look at related values:

• MCH (Mean Corpuscular Hemoglobin): Measures the average amount of hemoglobin in each red cell. High MCH often accompanies high MCV because larger cells hold more hemoglobin.
• MCHC (Mean Corpuscular Hemoglobin Concentration): Reflects how dense the hemoglobin is inside each red blood cell. This may stay normal even when MCV is elevated.
• RDW (Red Cell Distribution Width): Indicates the variation in red cell size. A high RDW with a high MCV can suggest mixed deficiencies or recovery from anemia.
• MPV (Mean Platelet Volume): While MCV looks at red cells, MPV measures average platelet size and can indicate how active the bone marrow is. People curious about both MCV and MPV can read my closely related guide on MPV blood test.

Together, these parameters help me and other clinicians determine whether a high MCV reflects nutritional deficiency, marrow stress, or medication effects.

Frequently Asked Questions

1. What does MCV blood test high mean?

Your red blood cells are larger than normal. Common causes include vitamin B12/folate deficiency, alcohol use, liver disease, or thyroid disorders.

2. Is it serious?

Usually not by itself, but persistent elevation needs evaluation to rule out treatable causes.

3. Can dehydration cause MCV blood test high?

No — dehydration affects plasma volume, not red cell size.

4. Can medications or alcohol raise MCV?

Yes. Anticonvulsants, chemotherapy drugs, and alcohol can enlarge red cells.

5. Can iron deficiency hide MCV blood test high?

Yes — mixed iron and B₁₂/folate deficiency may normalize MCV, so both iron and vitamin levels should be tested.

6. How long does it take to normalize?

Usually 1–4 months after treatment.

7. When should I repeat my test?

In 6–12 weeks, or earlier if symptoms worsen.

References

[1] Maner BS, Moosavi L. Mean Corpuscular Volume. StatPearls. Treasure Island (FL): StatPearls Publishing; 2024. https://www.ncbi.nlm.nih.gov/books/NBK545275/

[2] Kauffmann T. Macrocytosis. StatPearls. Treasure Island (FL): StatPearls Publishing; 2022. https://www.ncbi.nlm.nih.gov/books/NBK560908/

[3] Aslinia F, Mazza JJ, Yale SH. Megaloblastic anemia and other causes of macrocytosis. Clin Med Res. 2006 Sep; 4(3): 236-241. https://pmc.ncbi.nlm.nih.gov/articles/PMC1570488/

[4] Breedveld FC. The clinical significance of macrocytosis. Br J Haematol. 1981;49(3):353-8. https://pubmed.ncbi.nlm.nih.gov/7234509/

[5] O’Leary F, Samman S. Vitamin B12 in health and disease. Nutrients. 2010;2(3):299-316. https://pubmed.ncbi.nlm.nih.gov/22254022/

[6] Stabler SP. Vitamin B12 deficiency. N Engl J Med. 2013;368(2):149-60. https://pubmed.ncbi.nlm.nih.gov/23697526/

[7] Green R, Allen LH, Bjorke-Monsen AL, et al. Vitamin B₁₂ deficiency. N Engl J Med. 2017;377(2):149-60. https://pubmed.ncbi.nlm.nih.gov/28660890/

[8] Wu A, Chanarin I, Slavin G. Macrocytosis of chronic alcoholism. Lancet. 1974;303(7850):829-31. https://pubmed.ncbi.nlm.nih.gov/4132788/

[9] Seppä K, Heinilä K, Sillanaukee P, Saarni M. Evaluation of macrocytosis by general practitioners. J Stud Alcohol. 1996;57(1):97-100. https://pubmed.ncbi.nlm.nih.gov/8747507/

[10] Ballard HS. The hematological complications of alcoholism. Alcohol Health Res World. 1997;21(1):42-52. https://pubmed.ncbi.nlm.nih.gov/15706762/

[11] Horton L, Coburn RJ, England JM, Himsworth RL. The hematology of hypothyroidism. Q J Med. 1976;45(177):101-23. https://pubmed.ncbi.nlm.nih.gov/1257398/

[12] Martin GJ, Blazes DL, Mayers DL, Spooner KM. Stavudine-induced macrocytosis during therapy for human immunodeficiency virus infection. Clin Infect Dis. 1999;29(2):459-60. https://academic.oup.com/cid/article-abstract/29/2/459/274474?redirectedFrom=PDF

[13] Montalbán-Bravo G, García-Manero G. Myelodysplastic syndromes: 2018 update on diagnosis, risk-stratification and management. Am J Hematol. 2018;93(1):129-47. https://pubmed.ncbi.nlm.nih.gov/29214694/