The mean corpuscular volume is a part of a standard complete blood count.
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 (RDW).
The RDW is a statistical calculation made by automated analyzers that reflects the variability in size and shape of the RBCs.
To calculate MCV, the hematocrit (Hct) is divided by the concentration of RBCs ([RBC])[1]
Normally, MCV is expressed in femtoliters (fL, or 10−15 L), and [RBC] in millions per microliter (106 / μL).
If the hematocrit is expressed as a percentage, the red blood cell concentration as millions per microliter, and the MCV in femtoliters, the formula becomes
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.
[2] The normal reference range is typically 80-100 fL.
[3] In pernicious anemia (macrocytic), MCV can range up to 150 femtolitres.
Vitamin B12 and/or folic acid deficiency has also been associated with macrocytic anemia (high MCV numbers).
The most common causes of microcytic anemia are iron deficiency (due to inadequate dietary intake, gastrointestinal blood loss, or menstrual blood loss), thalassemia, sideroblastic anemia or chronic disease.
In some cases of thalassemia, the MCV may be low even though the patient is not iron deficient.
For a real world sized example, imagine you had 10 small jellybeans with a combined volume of 10 μL.
The 1 μL is only made of a proportion of red cells (e.g. 40%) with the rest of the volume composed of plasma.
Multiply by the hematocrit (a unitless quantity) to take this into account.
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: