The mean corpuscular volume, or mean cell volume, is a measure of the average volume of a red blood corpuscle. The measure is attained by multiplying a volume of blood by the proportion of blood that is cellular, and dividing that product by the number of erythrocytes in that volume. The mean corpuscular volume is a part of a standard complete blood count. In patients with anemia, it is the MCV measurement that allows classification as either a microcytic anemia, normocytic anemia or macrocytic anemia. Normocytic anemia is usually deemed so because the bone marrow has not yet responded with a change in cell volume. It occurs occasionally in acute conditions, namely blood loss and hemolysis. If the MCV was determined by automated equipment, the result can be compared to RBC morphology on a peripheral blood smear, where a normal RBC is about the size of a normal lymphocyte nucleus. Any deviation would usually be indicative of either faulty equipment or technician error, although there are some conditions that present with high MCV without megaloblastic cells. For further specification, it can be used to calculate red blood cell distribution width. The RDW is a statistical calculation made by automated analyzers that reflects the variability in size and shape of the RBCs.
Calculation
To calculate MCV, the hematocrit is divided by the concentration of RBCs Normally, MCV is expressed in femtoliters, and is the quantity expressed in millions per microliter. The normal range for MCV is 80–100 fL. For example, if the Hct = 42.5% and = 4.58 million per microliter, then The MCV can be determined in a number of ways by automatic analyzers. In volume-sensitive automated blood cell counters, such as the Coulter counter, the red cells pass one-by-one through a small aperture and generate a signal directly proportional to their volume. Other automated counters measure red blood cell volume by means of techniques that measure refracted, diffracted, or scattered light.
The MCV can be conceptualized as the total volume of a group of cells divided by the number of cells. For a real world sized example, imagine you had 10 small jellybeans with a combined volume of 10 µL. The mean volume of a jellybean in this group would be 10 µL / 10 jellybeans = 1 µL / jellybean. A similar calculation works for MCV. 1. Measure the RBC index in cells/µL. Take the reciprocal to convert it to µL/cell.
2. The 1 µL is only made of a proportion of red cells with the rest of the volumecomposed of plasma. Multiply by the hematocrit to take this into account. 3. Finally, convert the units of µL to fL by multiplying by. The result would look like this: Note: the shortcut proposed above just makes the units work out:
