Packed cell volume (PCV) is the portion of whole blood volume occupied by erythrocytes (red blood cells). PCV has traditionally been determined by measuring the height of the red cell volume in a micro-hematocrit capillary filled with whole blood, after centrifugation (see diagram). PCV is a directly measured value, whereas the hematocrit (Hct) is the corresponding calculated value, calculated by multiplying a red blood cell count (RBC count) with the mean erythrocyte volume (MCV). For most practical purposes PCV and Hct are interchangeable (and are frequently used as such by many authors), but typically PCV is slightly higher than the more accurate Hct due to plasma trapping (between the packed cells in a centrifuged capillary).