MCV blood test: normal range and what the result means

MCV (mean corpuscular volume) shows the average size of a single erythrocyte (red blood cell) in your blood sample. This index is calculated automatically by the analyser together with the other components of the complete blood count (CBC) — the red blood cell count, haemoglobin and haematocrit — and is one of the so-called red cell indices. This group also includes MCH (the mean amount of haemoglobin in a red blood cell) and MCHC (the mean haemoglobin concentration in the red blood cells). MCV helps the doctor classify the type of anaemia by red cell size: when the cells are smaller than usual (microcytic anaemia), iron deficiency or thalassaemia is suspected. When the cells are larger (macrocytic anaemia), a vitamin B12 or folate deficiency, or liver disease, is suspected. Normal-sized red blood cells with reduced haemoglobin (normocytic anaemia) point to other causes, for example a chronic illness or sudden blood loss. An MCV test is not done on its own — it is always part of the complete blood count.

• As part of a complete blood count (CBC) during a routine health check
• When you feel tired, weak, short of breath or dizzy — when anaemia is suspected
• To establish the type of anaemia and the direction of further testing (iron, B12, folate tests)
• To follow a known anaemia or blood disorder over time
• Before surgery or during treatment (for example chemotherapy), when blood counts are being monitored

How to prepare

• No special preparation is needed — if other blood tests are taken at the same time, your doctor may ask you not to eat for a few hours

Reference range

A raised MCV

A raised MCV, above the upper limit of the range, means the red blood cells are larger than usual — this is called macrocytic anaemia if haemoglobin is reduced at the same time. Possible causes are a vitamin B12 or folate deficiency, and also liver disease or thyroid disorders. Additional tests are needed to work out the cause.

• Vitamin B12 deficiency, including pernicious anaemia
• Folate deficiency
• Autoimmune diseases, coeliac disease or Crohn's disease, which interfere with B12 absorption
• Liver disease

What to discuss with a doctor when MCV is raised

• Vitamin B12 and folate tests, to establish the cause
• Liver markers (ALT, AST, GGT)
• A complete blood count over time — whether the change is progressing
• Diet and alcohol consumption habits are discussed with your doctor

A low MCV

A low MCV, below the lower limit of the range, means the red blood cells are smaller than usual — this is called microcytic anaemia if haemoglobin is reduced at the same time. The most common cause is iron deficiency anaemia; less often it is thalassaemia, an inherited blood disorder.

Causes of a low MCV

• Iron deficiency anaemia — the most common cause of a low MCV
• Thalassaemia — an inherited blood disorder that results in fewer healthy red blood cells

What to discuss with a doctor when MCV is low

• Iron, ferritin and transferrin saturation tests, to assess iron stores
• A possible cause of blood loss (periods, bleeding in the digestive tract)
• Family history for thalassaemia, if the iron markers are normal
• A complete blood count over time, to follow the change