Reviewed by Dr Simon Khela MBChB MRCGP, Medical Director, Private Medical Clinic
Receiving your blood test results can be confusing, especially when you come across unfamiliar abbreviations such as MCV. Many patients ask us, “What does MCV mean in a blood test?” or “Should I be worried if my MCV is high or low?”
The good news is that an abnormal MCV result doesn’t automatically mean you have a serious medical condition. It’s an important clue that helps doctors understand the size of your red blood cells and identify possible causes of symptoms such as tiredness, weakness or shortness of breath.
MCV is one of the measurements included in a Full Blood Count (FBC), one of the most commonly requested private blood tests in the UK. While MCV cannot diagnose a condition on its own, it plays an important role in identifying different types of anaemia, vitamin deficiencies and other health conditions that may require further investigation. If you’d like a broader primer first, our guide to decoding your blood test results is a good starting point.
MCV stands for Mean Corpuscular Volume, which measures the average size of your red blood cells.
Red blood cells carry oxygen from your lungs to every part of your body. If these cells are unusually small or unusually large, they may not function as efficiently, which can provide valuable clues about your overall health.
Your doctor may request an FBC if you’re experiencing symptoms such as persistent tiredness, fatigue, weakness, breathlessness, dizziness, pale skin, frequent headaches or difficulty concentrating. Many people, however, discover an abnormal MCV during routine health screening before any symptoms appear. Rather than providing a diagnosis, MCV helps doctors narrow down the possible causes of abnormal blood results and decide whether additional tests are needed.
Doctors use MCV to classify different types of anaemia, detect iron deficiency, identify vitamin B12 or folate deficiency, investigate chronic illnesses, assess the effects of certain medications, and decide which additional blood tests may help. Someone with fatigue and a low MCV may need iron studies, while someone with a high MCV may need vitamin B12 and folate testing — a structured approach that lets doctors investigate the cause rather than just treat the symptom.
In most UK laboratories, a normal MCV falls between 80 and 100 femtolitres (fL), though reference ranges vary slightly between labs depending on the equipment used.
A normal MCV usually means your red blood cells are an average size — but it doesn’t always mean everything is normal. Someone can still have anaemia, blood loss, chronic inflammation, kidney disease or an early nutritional deficiency with a normal MCV. This is why doctors always interpret MCV alongside other results: haemoglobin (Hb), red blood cell (RBC) count, mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), and red cell distribution width (RDW).
A low MCV — microcytosis — means your red blood cells are smaller than normal. Small red blood cells often carry less haemoglobin, making it harder for your body to transport oxygen efficiently, which can contribute to fatigue, reduced exercise tolerance, weakness, dizziness, breathlessness or pale skin. Some people have no symptoms at all and only discover a low MCV during routine testing.
Iron deficiency is the most common cause. Iron is essential for producing haemoglobin, and deficiency can result from heavy menstrual bleeding, pregnancy, poor dietary intake, gastrointestinal bleeding, stomach ulcers, coeliac disease, or inflammatory bowel disease. Your GP will usually recommend a ferritin test to confirm iron deficiency.
Another common cause is thalassaemia trait, an inherited condition affecting haemoglobin production. Unlike iron deficiency, people with thalassaemia trait usually feel completely well, have lifelong low MCV results, and don’t need treatment — distinguishing it from iron deficiency matters, since unnecessary iron supplements won’t help thalassaemia.
Anaemia of chronic disease can also cause a low or borderline MCV, seen in long-term inflammatory conditions such as rheumatoid arthritis, chronic kidney disease, chronic infections or autoimmune conditions — here, inflammation affects how the body uses and stores iron rather than causing an actual shortage.
Less common causes include sideroblastic anaemia, lead poisoning, and certain inherited blood disorders, usually identified once the more common causes have been ruled out.
No — this is one of the most common misconceptions patients have after reviewing results online. Doctors often request ferritin, iron studies, vitamin B12, folate, inflammatory markers, or haemoglobin electrophoresis (if thalassaemia is suspected) before confirming a cause. Treating a low MCV without identifying the underlying reason can delay the diagnosis of something that needs a different approach — even if you feel completely well, an abnormal result is worth discussing at a GP appointment.
A high MCV — macrocytosis — means your red blood cells are larger than normal. Unlike a low MCV, this doesn’t necessarily indicate anaemia; some people have a raised MCV with a normal haemoglobin level. Symptoms, when present, can include persistent tiredness, fatigue, weakness, breathlessness, pale skin, difficulty concentrating, tingling or numbness in the hands and feet, poor balance or memory problems.
One of the most common causes is vitamin B12 deficiency. B12 is essential for healthy red blood cell production and a healthy nervous system; without enough of it, the body produces fewer but larger red blood cells. People with B12 deficiency may also notice pins and needles, numbness, memory difficulties, mood changes, balance problems or a sore tongue. Early diagnosis matters, since untreated B12 deficiency can occasionally cause permanent nerve damage. We offer vitamin B12 injections where clinically appropriate, and our guide on vitamin B12 deficiency: symptoms, food sources and treatment covers this in more depth.
Folate (vitamin B9) plays a similar role. Low folate can result from a poor diet — including a strictly vegan diet without adequate supplementation — pregnancy, coeliac disease, certain medications, or excessive alcohol consumption. It’s usually straightforward to diagnose and treat once identified.
Regular alcohol intake is another common reason for a raised MCV: alcohol can affect the bone marrow and interfere with red blood cell production even before liver function tests become abnormal. Reducing alcohol intake — our piece on alcohol consumption and its impact on your health explains the wider picture — often allows MCV to normalise over several months.
Liver disease, hypothyroidism, and certain medications (methotrexate, hydroxyurea, some chemotherapy drugs, and some anti-epileptics) round out the common causes; your doctor will factor in your medication history when interpreting the result.
MCV is only one part of your FBC. To understand why it’s high or low, doctors usually interpret it alongside haemoglobin (anaemia and severity), ferritin (iron stores), vitamin B12 and folate (nutritional deficiencies), red blood cell count, MCH/MCHC (haemoglobin content per cell), red cell distribution width (RDW, which helps distinguish anaemia types and spot mixed deficiencies), and sometimes a reticulocyte count (immature red blood cells, showing whether the bone marrow is producing cells normally).
Yes — this surprises many patients. Some people have normocytic anaemia, where red blood cells are a normal size but there simply aren’t enough of them. Common causes include chronic kidney disease, acute blood loss, chronic inflammation, and some long-term medical conditions. This is exactly why doctors never interpret MCV in isolation.
Speak to your GP if your MCV remains abnormal on repeat testing, you have persistent fatigue or weakness, unexplained weight loss, numbness or tingling, increasing breathlessness, heavy menstrual bleeding, or a family history of inherited blood disorders. Early investigation usually identifies straightforward, treatable causes like iron or vitamin deficiencies. If it’s easier, a home visit can be arranged instead of a clinic appointment, and more complex results can lead to a specialist referral to a haematologist.
Treatment depends entirely on the underlying cause, not the number itself:
Attempting to treat an abnormal MCV without identifying the cause may delay an important diagnosis.
“One of the most common questions I hear from patients is, ‘Should I be worried about my MCV result?’ The answer is that MCV is a useful indicator, not a diagnosis. It’s natural to feel concerned seeing a result marked ‘high’ or ‘low’, but these changes are often caused by common, treatable conditions like iron, B12, or folate deficiency. Rather than fixating on a single number, we look at the complete picture — your symptoms, history, and the rest of your blood results. If your MCV is outside range, don’t panic, but do get it discussed properly.”
MCV is measured as part of a standard Full Blood Count, taken from a routine blood sample. It’s often included within a general health check-up and is also a standard component of many pre-employment medical assessments. We offer private blood testing across the UK, including London, Birmingham, Leicester, Newcastle, Oxford, Derby, Sutton Coldfield and Bournemouth & Dorset. Our guide on how long blood test results take explains typical turnaround, and full pricing is on our fees page.
· MCV (Mean Corpuscular Volume) measures the average size of your red blood cells.
· It forms part of a routine Full Blood Count (FBC).
· A low MCV commonly suggests iron deficiency or thalassaemia trait.
· A high MCV may be linked to vitamin B12 deficiency, folate deficiency, alcohol use, liver disease or hypothyroidism.
· A normal MCV does not always mean your blood test is normal.
· MCV should always be interpreted alongside other blood test results and your clinical symptoms.
· Most causes of abnormal MCV can be investigated with additional blood tests and are often treatable.
· Decoding your blood test: a guide to understanding your results
· How long do blood test results take? A comprehensive guide for UK patients
· Bone profile blood test: everything you need to know
· Vitamin B12: a vital nutrient for your health
· Coeliac disease: causes, symptoms and how we can help
· Rheumatoid arthritis: symptoms, causes, treatment
· Dry January 2026: health benefits of quitting alcohol
MCV stands for Mean Corpuscular Volume, which measures the average size of your red blood cells.
A normal MCV is usually between 80 and 100 femtolitres (fL), although reference ranges may vary slightly between laboratories.
Not always. A high MCV may result from vitamin B12 deficiency, folate deficiency, alcohol consumption or certain medical conditions. Your doctor will assess it alongside other blood test results.
No. While iron deficiency is the most common cause, low MCV can also occur with thalassaemia trait, chronic inflammatory conditions and some inherited blood disorders.
Dehydration has little direct effect on MCV but may influence other blood test measurements. Your doctor will interpret the results in the context of your overall health.
Yes. Regular alcohol consumption can cause larger red blood cells and may lead to a raised MCV, even if liver function tests are normal.
Yes. Vitamin B12 deficiency is one of the most common causes of macrocytosis (high MCV) and should be investigated promptly.
Yes. Some forms of anaemia, known as normocytic anaemia, occur despite a normal MCV.
This depends on the underlying cause. Once treated, MCV often improves over several weeks to months as new red blood cells are produced.
A mildly abnormal MCV is often not a cause for concern, but it should always be reviewed by your GP alongside your symptoms and other blood test results to determine whether further investigation is needed.
Same Day Online Booking
No Time Limits Appointments
Online Consultations Available
Latest Blog Posts
What Does RDW Mean in a Blood Test? Causes of High and Low RDW Explained
What Is a Creatinine Blood Test? Results, Normal Ranges & What They Mean
Abnormal Blood Test Results: Common Causes Explained
What Is a Ferritin Blood Test? Meaning, Results and What's Normal
What Is an HbA1c Blood Test? Meaning, Results and What's Normal
Diabetes: Your Comprehensive Look At This Chronic Condition
Ready to take the next step?
Before you go
STRUGGLING WITH HAYFEVER THIS SEASON?
Our hayfever treatment is fast, effective often providing relief within 24 hours.
Book Hayfever Treatment →Book a Hayfever Appointment