Hematocrit or packed cell volume (PCV) - is the fraction of whole blood volume that consists of red blood cells.
Technique
After centrifugation, the height of the red cell column is measured and compared to the total height of the column of whole blood. The percentage of the total blood volume occupied by the red cell mass is the hematocrit. Hematocrit depends mostly on the number of RBCs but there is some effect (to a much lower extent) from the average size of the RBCs.
Reference values
Reference values are 42-52% for males and 36-48% for females. The hematocrit is usually about 3 times the hemoglobin value (assuming there is not marked hypochromia). The average error in hematocrit is about 1-2%. The hematocrit may be changed by altitude, position, and heavy smoking, in the same manner as the hemoglobin may be changed.