Packed cell volume (PCV) or Hematocrit (%) of animals
Packed cell volume (PCV) or Hematocrit (%) is percent volume of packed blood cells present in whole blood after centrifugation at 3000 rpm for 30 minutes.
Hematocrit is measured by two methods:
- Wintrobe hematocrit (macro method)
- Microhematocrit method
Wintrobe hematocrit (macro method)
Wintrobe tubes have uniform 3 mm bore, calibrated by 10 cm scales with millimetre divisions. The wintrobe pipette with a long but narrow delivery tube is used to fill about 1 ml of blood into the wintrobe tube without air bubbles.
Horse and dog blood require a relative centrifugal force of 2,260 G (generally 3000 rpm) for 30 minutes, while it is for 60 minutes in the case of cattle and pig blood. The blood of sheep and goat require higher relative centrifugal force than 2,260 G.
True PCV = Venous PCV x 0.96 (correction factor for trapped plasma)
The RBCs settle to the bottom of the hematocrit tube leaving the plasma above the packed erythrocytes. A thin white or yellow layer called the buffy coat occurs in between these two and it indicates the WBC or the leukocytes.
The amount of trapped plasma in the erythrocyte column varies with PCV, size of erythrocytes and the degree of rouleaux formation. Canine blood is characterised by large blood cells and greater tendency for rouleaux formation. Similarly equine blood is characterised by extreme rouleaux formation, hence less plasma is trapped.
Microhematocrit method
PCV may be estimated by blood filled capillary tubes (32 mm x 0.8 mm) centrifuged at 14,000 G for 2 minutes. In general, the PCV is approximately three times the Hb concentration. PCV values ranges between 38 to 45% in most of the domestic animals.
Factors influencing PCV are: High temperature, muscular exercise, stress, pregnancy, haemorrhage, dehydration and burns, anemia, polycythemia and leukemia.
Normal PCV values in domestic animals
| Species | PCV ( % ) |
| Dog | 37-55 (45) |
| Cat | 24-45 (37) |
| Cow | 24-46 (35) |
| Sheep | 24-50 (38) |
| Goat | 19-38 (28) |
| Horse | 32-52 (42) |
| Pig | 32-50 (42) |