Mean Cell Volume (MCV) is Directly Measured by Most Automated Blood Cell Counting Instruments
The mean cell volume (MCV) is the parameter that is directly measured by most automated blood cell counting instruments. 1, 2, 3
How Automated Blood Cell Counters Work
Modern automated hematology analyzers directly measure:
- Mean Cell Volume (MCV) - using electrical impedance or light scattering technology
- Red Blood Cell (RBC) count
- Hemoglobin concentration (Hgb) - through spectrophotometric methods
From these direct measurements, other parameters are calculated:
- Hematocrit (HCT) = RBC × MCV
- Mean Cell Hemoglobin (MCH) = Hgb ÷ RBC
- Mean Cell Hemoglobin Concentration (MCHC) = Hgb ÷ HCT
Evidence for Direct Measurement of MCV
Automated cell counters directly measure the volume of individual red blood cells as they pass through the analyzer 4. This is accomplished through:
- Electrical impedance (Coulter principle): Cells passing through an aperture cause measurable changes in electrical resistance proportional to their volume
- Light scattering: Laser-based systems measure the scatter pattern of light as cells pass through a flow cell
Multiple studies comparing different hematology analyzers consistently show that MCV is directly measured, while other parameters like MCHC are calculated from the primary measurements 2, 3.
Why Other Options Are Not Directly Measured
- Hemoglobin: Measured spectrophotometrically after RBC lysis, but is a separate measurement from the cell counting process 3
- Absolute lymphocyte count: Derived from the total WBC count and the differential percentage of lymphocytes 5
- Mean cell hemoglobin concentration (MCHC): Calculated as the ratio of hemoglobin to hematocrit (Hgb/HCT) 1
Clinical Significance
The direct measurement of MCV provides important diagnostic information:
- Microcytosis (low MCV) suggests iron deficiency, thalassemia, or anemia of chronic disease 5
- Macrocytosis (high MCV) suggests vitamin B12/folate deficiency, liver disease, or certain medications 5
- MCV is more reliable than calculated parameters and is less affected by sample storage conditions 1
Common Pitfalls in Interpretation
- MCV measurement can be affected by cellular deformability and other factors 4
- Different analyzers may show variations in MCV measurements (typically within 5% of mean value) 3
- MCV should be interpreted alongside other parameters like RDW (Red cell Distribution Width) for comprehensive assessment 6
In summary, MCV is directly measured by automated blood cell counters, while parameters like MCHC and absolute lymphocyte count are calculated from other measurements.