MCV - Mean Corpuscular Volume
Mean cell volume (MCV) - individual cell size is the best index for classifying anemias. This index expresses the volume occupied by a single erythrocyte and is a measure in cubic micrometers (femtoliters, or fL) of the mean volume. The MCV indicates whether the red blood cell size appears normal (normocytic), smaller than normal (80 µm3, microcytic), or larger than normal (100 µm3, macrocytic).
The MCV is the average volume of an RBC in femtoliters (fL). One fL = one cubic micrometer (μm3). The MCV is calculated manually by dividing the volume of packed red cells (hematocrit) by the number of red cells, using the formula:
MCV (fL) = Hematocrit (in %) × 10 / RBC ( in 1012/L)
Example: If the Hct is 45% and the red cell count is 5 × 1012 cells per liter:
MCV (fL) = 45 (%) × 10 / 5 × 1012/L = 90 fL
The MCV indicates whether the RBCs will appear small (microcytic), normal (normocytic), or large (macrocytic). If the MCV is less than 80 fL, the RBCs will be microcytic. If it is greater than 100 f L, the RBCs will be macrocytic. If it is within the normal range, the RBCs will be normocytic.
The chief source of error in the MCV is the considerable error in the manual red cell count, if used. With automated cell counters and electronically calculated indices, the MCV is measured directly, and the hematocrit is calculated from MCV and red cell count (Hct = MCV × RBC). The MCV is now considered the most reliable automated index and is probably the most effective discriminant for the classification of anemias.
The MCV in normal adults is between 80 and 96 fL.
When there is a decrease in the mean corpuscular volume, the erythrocytes are microcytic, or smaller than normal. Microcytic red blood cells are seen in iron deficiency anemia, lead poisoning, and thalassemia. In microcytic anemia with marked iron deficiency, it may be 60 to 70 fL.
An increase in the mean corpuscular volume indicates that the red blood cells are macrocytic, or larger than normal. Pernicious anemia is associated with macrocytic red blood cells. In some macrocytic anemias (e.g., pernicious anemia) the MCV may be as high as 150 fL. When the mean corpuscular volume is within normal range, the red blood cells are normocytic, or of normal size. Aplastic, hemolytic, and temporary blood loss anemia are associated with red blood cells that are normal in size.
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