Hematologist
CION Cancer Clinics
When large red cells point to a marrow problem | CION Cancer Clinics
Most high MCV results are not a marrow problem. Large red cells usually come from low B12 or folate, alcohol, liver or thyroid trouble, or a medicine. A marrow condition such as MDS becomes more likely when white cells or platelets are also low, the simple causes are ruled out, or the MCV stays high after treatment. This page explains the patterns, the usual tests and what one result cannot tell you. At CION Cancer Clinics, our haematologist cares for anaemia, bleeding, clotting and inherited blood disorders, with ArogyaSri, CGHS and cashless insurance accepted.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- When is a high MCV a sign of a marrow problem?
- What usually makes red cells large?
- Which report patterns point towards the marrow?
- What tests will your doctor usually order?
- What is MDS, and who does it usually affect?
- What do people often get wrong about a high MCV?
- Common questions about a high MCV and MDS
The short answer
When is a high MCV a sign of a marrow problem?
Most high MCV results are not a marrow problem. Large red cells usually come from low vitamin B12 or folate, alcohol, liver disease, an underactive thyroid or a medicine. A marrow problem such as MDS becomes more likely when the large red cells come with other low counts, the usual causes are ruled out, or the result does not settle once they are treated.
What MCV means on your report
MCV stands for mean cell volume. It is the average size of your red blood cells. When it sits above the normal range printed on your report, doctors call it macrocytosis, which simply means large red cells. Normal ranges differ between laboratories, so always read your number against the range your own lab has printed beside it.
Why size gives a clue
Red cells are made in the bone marrow, the soft tissue inside your bones. To divide properly, the marrow needs B12 and folate. When they run short, or when the marrow itself is not working normally, cells come out larger than they should. So a large MCV tells your doctor where to look. It does not tell anyone which of those reasons is yours.
What this page cannot tell you
No single MCV result can diagnose or rule out MDS. The answer comes from your full blood count, a look at your blood under a microscope, your other tests and your symptoms, read together, and sometimes a marrow test.
One high result is read alongside a repeat test. Do not decide what it means from the number alone.Checked first
What usually makes red cells large?
Your doctor works through these before thinking about the marrow, because they are far more common and most can be put right.
Low B12 or folate
The most common reason in India, especially in families who eat little or no meat, fish, eggs or dairy. It often comes with tiredness, a sore tongue or tingling in the feet.
Tested with
- Serum B12 level
- Folate level
Alcohol and the liver
Regular drinking raises the MCV even when the liver tests look normal. Fatty liver and other liver disease can do the same. The size often comes down slowly once drinking stops.
An underactive thyroid
A slow thyroid can enlarge red cells a little. A simple thyroid blood test answers this question, and it is usually ordered alongside the vitamin tests.
Medicines
Some medicines for diabetes, seizures, arthritis, HIV and cancer can raise the MCV. Tell your doctor everything you take. Never stop a prescribed medicine on your own because of this result.
Young red cells after bleeding
After a bleed, or when red cells break down early, the marrow releases young cells that are larger. A reticulocyte count, which measures these young cells, shows whether this is happening.
Not sure whether this applies to you?
Ask an oncologistReading the pattern
Which report patterns point towards the marrow?
More often a simple cause
Worth a haematologist's review
Only the MCV is high; white cells and platelets are normal
White cells or platelets are also low
B12 or folate is low, and the count improves after treatment
B12, folate and thyroid are normal, or treatment changes nothing
A clear reason such as alcohol or a known medicine
No reason found, and the MCV stays high on repeat tests
The blood film shows large but otherwise normal-looking cells
The film shows oddly shaped cells or immature white cells
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When not to wait for an appointment
If you have a high MCV and also a fever with shivering, bleeding that will not stop, many new bruises or tiny red spots on the skin, or sudden severe breathlessness, go to the nearest emergency department the same day or call 108. Take your latest blood report with you. These can be signs that more than one blood count has dropped.
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What happens next
What tests will your doctor usually order?
Repeat the full blood count
A single result can be thrown off by a delayed sample or a recent illness. A repeat test shows whether the high MCV is real, and whether the other counts are moving with it.
Check the simple causes
B12, folate, thyroid and liver tests, and a reticulocyte count. Your doctor will also ask about alcohol and every medicine you take, including ones bought without a prescription.
Look at the blood film
A trained person looks at your blood under a microscope. Oddly shaped red cells, or white cells that look immature, change the question from "which vitamin?" to "is the marrow healthy?"
A marrow test, if needed
If the pattern still points to the marrow, a small sample is taken from the back of the hip bone under local numbing. This is the test that confirms or rules out MDS.
If the marrow is the question
What is MDS, and who does it usually affect?
MDS stands for myelodysplastic syndromes. In plain terms, the marrow makes blood cells that do not grow up properly, so fewer healthy cells reach the blood. It is a type of blood cancer, though many forms grow slowly and some people need only regular monitoring for a long time.
Who it tends to affect
MDS is mostly seen in older adults and is uncommon in young people. It is more likely in someone who has had chemotherapy or radiotherapy for an earlier cancer, or long exposure to chemicals such as benzene. Being older and having a high MCV does not mean you have it. Most older adults with large red cells turn out to have one of the common causes.
Why a haematologist should see the full picture
MDS covers several different conditions with very different outlooks. The marrow report, chromosome tests and your blood counts together decide which type it is and whether treatment is needed now. At CION, the haematology team reviews these reports, discusses the case at a tumour board and coordinates any specialised marrow tests with qualified laboratories. Ask your doctor which laboratory will read your sample and when the chromosome results are expected.
Nothing on this page can tell you your own outlook. That conversation belongs with the haematologist who has your reports.Commonly believed
What do people often get wrong about a high MCV?
"A high MCV means blood cancer."
It usually does not. Low B12 or folate, alcohol, thyroid and liver problems, and medicines are all far more common. The result is a reason to look for the cause, calmly and in order, not a diagnosis in itself.
"My haemoglobin is normal, so the MCV does not matter."
Large red cells can appear before haemoglobin falls. A high MCV on its own is still worth explaining, especially if it stays high on repeat tests or the white cells or platelets are drifting down.
"I will just take B12 tablets and see."
Starting vitamins before the blood tests are drawn can hide what was low and make the picture harder to read. Ask your doctor to test first. If B12 treatment is started and the count does not improve, that itself is useful information.
"A bone marrow test is dangerous, so we will avoid it."
It is done under local numbing and most people go home the same day. It can be sore for a few days. When the pattern points to the marrow, avoiding the test only delays an answer.
Questions we are asked
Common questions about a high MCV and MDS
My MCV is only slightly high. Should I worry?
A result just above your lab's range, with normal haemoglobin, white cells and platelets, is very often from B12, folate, alcohol or a medicine. It still deserves a repeat test and a check of the simple causes. What matters more is the direction over time and what the other counts are doing.
Can MDS be found with a normal MCV?
Yes. Large red cells are common in MDS, but not present in everyone. Some people show only a low platelet count or a low white cell count at first. That is why a haematologist looks at the whole blood count and the blood film, not the MCV alone.
Which doctor should I see about a high MCV?
Your family doctor or physician can usually start with the simple tests. Ask for a haematologist's opinion if other counts are also low, the film shows abnormal cells, or no cause is found. At CION, Dr. Basudev Pokhrel, our haematologist, reviews such reports and explains the next step.
My father is over 70 with a high MCV. Is that just age?
Age alone does not raise the MCV. In an older person, the common causes are still the most likely, but MDS is also more common with age. So the result should be explained, not put down to age. Take his previous reports and medicine list to the appointment.
Does a bone marrow test hurt?
The skin and bone surface are numbed first. Most people feel pressure and a short, sharp pulling feeling when the liquid marrow is drawn. The area can ache for a few days afterwards. Tell the team if you are on a blood thinner before the test, and let them decide what to do.
If it is MDS, does it always need treatment straight away?
No. Some lower-risk types are watched with regular blood counts, and treatment starts only if counts fall or symptoms appear. Other types need treatment sooner. The marrow and chromosome results decide which group you are in, so ask your haematologist to explain your type in plain words.
Can stopping alcohol bring my MCV down?
If alcohol is the cause, the MCV usually comes down gradually after drinking stops, because the body replaces red cells slowly. If it stays high after a long gap from alcohol, and vitamins and thyroid are normal, tell your doctor. That is a reason to look further.
What should I bring to a haematology appointment?
Bring every blood count you have, old ones too, so the doctor can see the trend. Add your B12, folate, thyroid and liver results, a list of all medicines, and any earlier chemotherapy or radiotherapy records. If a family member helps you decide, bring them along.
Your Haematologist
Meet CION's haematologist. One specialist for your blood report and your plan.
Dr. Basudev Pokhrel reviews blood counts, transfusion needs and blood disorders, and works with the CION tumour board on blood cancers.
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Sources
- NHS — Vitamin B12 or folate deficiency anaemia
- Cancer Research UK — Myelodysplastic syndromes (MDS)
- National Cancer Institute — Myelodysplastic Syndromes Treatment (PDQ), patient version
- Blood Cancer UK — Myelodysplastic syndromes (MDS)
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Macrocytosis Without AnaemiaIf your haemoglobin is still normalReading a B12 Result and Borderline ValuesThe first cause your doctor checksFolate Deficiency and Who Gets ItThe other vitamin behind large red cellsBlood cancer guideIf the marrow turns out to be the questionB12, Folate and Macrocytic AnaemiaThe full guide to this group of conditions
Talk to us
Holding a report with a high MCV?
Tell us what has been found so far. Our haematology team will read the reports with you and explain the next step. One helpline serves every CION centre.