Mean Cell Volume (MCV)

What it is

Mean Cell Volume, or MCV, is a measurement found within a Full Blood Count (FBC) blood test. It tells us about the average size of your red blood cells. Red blood cells are the tiny cells in your blood responsible for carrying oxygen from your lungs to all parts of your body, and then carrying carbon dioxide back to your lungs to be exhaled.

The MCV is measured in a unit called femtolitres (fl), which is a tiny unit of volume. The typical range for MCV in adults in the UK is generally between 76 and 100 fl. This means that for most people, their red blood cells fall within this average size.

Why it matters

The size of your red blood cells can give valuable clues about your overall health and the health of your blood. If your MCV is outside the typical range, it might suggest that your body isn't producing red blood cells as effectively as it should, or that there's an issue with how they are being used or destroyed.

An MCV that is consistently higher or lower than the normal range can be an early indicator of certain conditions, particularly different types of anaemia. Anaemia is a condition where you don't have enough healthy red blood cells to carry adequate oxygen to your body's tissues, which can lead to tiredness and weakness.

Understanding your MCV can help your doctor investigate the cause of any symptoms you might be experiencing and guide them towards the most appropriate course of action.

What can cause it to be high or low

An MCV reading that falls outside the 76–100 fl range can be associated with various factors.

High MCV (Macrocytosis): This means your red blood cells are, on average, larger than normal. This can be linked to:

• Vitamin deficiencies: A lack of vitamin B12 or folate (also known as folic acid) is a common cause. These vitamins are essential for the production of healthy red blood cells.
• Liver disease: Certain liver conditions can affect red blood cell production and size.
• Alcohol intake: Heavy or regular alcohol consumption can impact red blood cell production.
• Hypothyroidism: An underactive thyroid gland can sometimes lead to larger red blood cells.
• Certain medications: Some medicines can influence red blood cell size.
• Myelodysplastic syndromes (MDS): These are a group of disorders where the bone marrow doesn't produce enough healthy blood cells.

Low MCV (Microcytosis): This means your red blood cells are, on average, smaller than normal. This is often associated with:

• Iron deficiency anaemia: This is the most common cause. Iron is a crucial component of haemoglobin, the protein in red blood cells that carries oxygen. Without enough iron, red blood cells are smaller and paler.
• Thalassaemia: This is an inherited blood disorder that affects the production of haemoglobin, leading to smaller red blood cells.
• Anaemia of chronic disease: Long-term illnesses can sometimes affect red blood cell production.
• Lead poisoning: Exposure to lead can interfere with red blood cell formation.

It's important to remember that an abnormal MCV reading doesn't automatically mean you have a serious condition. It's a signpost that prompts further investigation.

Lifestyle factors that may help

While medical conditions are the primary drivers of MCV changes, certain lifestyle choices can play a supportive role, particularly in managing deficiencies or optimising overall blood health. Discussing these with your GP is always the best first step.

• Diet: A balanced diet rich in essential vitamins and minerals is fundamental. Foods high in iron, vitamin B12, and folate are particularly important for red blood cell production. This can include leafy green vegetables, red meat, fish, eggs, and fortified cereals.
• Alcohol consumption: Limiting alcohol intake can be beneficial, as excessive alcohol can negatively impact red blood cell production.
• Smoking: While not directly linked to MCV in the same way as deficiencies, smoking can affect overall cardiovascular health and oxygen transport, which is indirectly related to the function of red blood cells.

Questions to discuss with your GP

If your MCV result is outside the typical range, or if you have concerns about your red blood cell health, your GP is the best person to talk to. Here are some questions you might consider discussing:

• What does my specific MCV result mean in the context of my overall health?
• Are there any other blood test results that, when combined with my MCV, suggest a particular cause?
• Could my symptoms, such as tiredness or shortness of breath, be related to my MCV?
• What further tests might be needed to understand the reason for my MCV being high or low?
• Are there any dietary changes or lifestyle adjustments you would recommend for me to consider?
• What is the plan for monitoring my MCV in the future?