Manual PCV/ HCT Test

Principle

The principle behind the manual packed cell volume (PCV) or hematocrit test is sedimentation and separation of blood components based on density:
– Whole blood contains solid components like red blood cells, white blood cells and platelets suspended in liquid plasma.
– The components have different densities – red cells are densest, white cells intermediate and plasma is the least dense.
– When blood is spun in a high speed centrifuge, the cells get packed based on their density gradients.
– Denser red cells get packed at the bottom, white cells form a buffy layer above this and plasma stays at the top.
– The volume occupied by packed red cells compared to the total volume of whole blood gives the PCV or hematocrit ratio.
– Hematocrit is the percentage of red cell volume compared to total blood volume.
– It correlates with the number of erythrocytes and the hemoglobin concentration.

In summary, the hematocrit test allows estimation of red cell mass by measurement of packed red cell volume following high speed centrifugation and separation of blood components based on density differences.