Mean corpuscular volume

The mean corpuscular volume, or "mean cell volume" (MCV), is a measure of the average red blood cell volume (i.e. size) that is reported as part of a standard complete blood count.

In patients with anemia, it is the MCV measurement that allows classification as either a microcytic anemia (MCV below normal range) or macrocytic anemia (MCV above normal range).

Calculation

It can be calculated (in litres) by dividing the hematocrit by the red blood cell count (number of red blood cells per litre). The result is typically reported in femtolitres.

If the MCV was determined by automated equipment, the result can be compared to RBC morphology on a peripheral blood smear. Any deviation would be indicative of either faulty equipment or technician error.

For further specification, it can be used to calculate red blood cell distribution width (RDW).

Interpretation

The normal reference range is typically 80-100 fL^[1].

High

In presence of hemolytic anaemia, presence of reticulocytes can increase MCV. In pernicious anemia (macrocytic), MCV can range up to 150 femtolitres. An elevated MCV is also associated with alcoholism^[2] (as are an elevated GGT and a ratio of AST:ALT of 2:1). Vitamin B12 and/or Folic Acid deficiency has also been associated with macrocytic anemia (high MCV numbers).

Low

The most common causes of microcytic anemia are iron deficiency (due to inadequate dietary intake, gastrointestinal blood loss, or menstrual blood loss), thalassemia, or chronic disease.

A low MCV number in a patient with a positive stool guaiac test (bloody stool) is highly suggestive of GI cancer.

In iron deficiency anemia (microcytic anemia), it can be as low as 60 to 70 femtolitres. In cases of thalassemia, the MCV may be low even though the patient is not iron deficient.

Worked example

References

See also

• Anemia: Differential Diagnosis
• Full blood count
• Mean corpuscular hemoglobin