Mean corpuscular volume

To calculate MCV, the hematocrit (Hct) is divided by the concentration of RBCs ([RBC]) [1]

${\displaystyle {\textit {MCV}}={\frac {\textit {Hct}}{[{\text{RBC}}]}}}$

Normally, MCV is expressed in femtoliters (fL, or 10⁻¹⁵ L), and [RBC] in millions per microliter (10⁶ / μL). The normal range for MCV is 80–100 fL.

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

${\displaystyle {\textit {MCV}}/\mathrm {L} ={\frac {{\mathit {Hct\%}}/100}{[{\text{RBCmmL}}]\times (10^{6}/10^{-6})/\mathrm {L} ^{-1}}}}$

${\displaystyle {\textit {MCV}}/\mathrm {fL} ={\textit {MCV}}/(10^{-15}\,\mathrm {L} )=10^{15}{\frac {{\mathit {Hct\%}}/100}{[{\text{RBCmmL}}]\times 10^{12}}}={\frac {{\mathit {Hct\%}}\times 10}{[{\text{RBCmmL}}]}}}$

For example, if the Hct = 42.5% and [RBC] = 4.58 million per microliter (4,580,000/μL), then

${\displaystyle {\textit {MCV}}={\frac {0.425}{4.58\cdot 10^{6}/(10^{-6}\,\mathrm {L} )}}=92.8\cdot 10^{-15}\,\mathrm {L} =92.8\,\mathrm {fL} }$

Using implied units,

${\displaystyle {\textit {MCV}}/{\textrm {fL}}={\frac {42.5\times 10}{4.58}}=92.8}$

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]

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 (1/RBC index) to convert it to µL/cell.

${\displaystyle {\frac {1}{5\times 10^{6}}}\ \mathrm {\mu L/cell} =2\times 10^{-7}\ \mathrm {\mu L/cell} }$

2. 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.

${\displaystyle 2\times 10^{-7}\ \mathrm {\mu L/cell} \times 0.4=8\times 10^{-8}\ \mathrm {\mu L/cell} }$

3. Finally, convert the units of µL to fL by multiplying by ${\displaystyle 10^{9}}$. The result would look like this:

${\displaystyle 8\times 10^{-8}\ \mathrm {\mu L/cell} \times {\frac {10^{9}\ \mathrm {fL} }{1\ \mathrm {\mu L} }}=80\ {\frac {\mathrm {fL} }{\mathrm {cell} }}}$

Note: the shortcut proposed above just makes the units work out: ${\displaystyle 10\times 40\div 5=80}$