Which formula is used to calculate MCV?

• A. Hb (g/dl) x 10 / Total RBC count
• B. Hb (g/dl) x 50 / PCV%
• C. Hb (g/dl) x 100 / Total RBC count
• D. PCV x 10 / Total RBC count

Answer: (D)

MCV reflects the average size of red blood cells by relating how much of the blood is made up of red cells (hematocrit or PCV) to how many red cells are present. The standard way to compute it is to take the hematocrit percentage, multiply by 10, and then divide by the RBC count (in millions per microliter). This yields MCV in femtoliters per cell. The reason this works is that hematocrit indicates total red cell volume in a given blood sample, while the RBC count tells you how many cells share that volume; dividing the total volume by the number of cells gives the average cell volume. For example, if PCV is 45% and the RBC count is 5.0 million/µL, MCV = (45 × 10) / 5 = 90 fL, which is normal. Using hemoglobin in the numerator or other incorrect denominators does not measure the size of each individual red blood cell, so those formulas do not yield MCV.