Determination of packed cell volume (PCV)/ Hematocrit (Hct)

 

Apparatus and reagents

  • Anticoagulant added blood sample
  • Pasteur pipette
  • Wintrobe tube
  • centrifuge machine

Wintrobe method


Principle


A sample of blood to which an anticoagulant has been added is centrifuged in a hematocrit tube. The RBCs are packed towards the bottom of the tube by the centrifugal force as these are heavier than the liquid plasma. PCV represents the volume of the cells per unit volume of the whole blood and is expressed as a percentage.

Procedure


  1. Fill the wintrobe tube with blood, using a Pasteur pipette, starting at its bottom and withdrawing the a pipette as the tube is filled from below upwards.
  2. Bring the blood column to the “O” mark.
  3. Remove air bubbles, if any, from the top of the column of blood so that it stands exactly at “O”.
  4. Centrifuge the tube for about 20 minutes at 2500 rpm.
  5. Take the reading of the packed cells and centrifuge the tube again for 5 minutes and note the reading.
  6. Repeat the procedure if there is a difference.
  7. Record the final reading when three consecutive readings are identical i.e. when the red cells have been fully packed.

Observation and result


  • The upper level of the packed red cells is quite sharply and distinctly visible.
  • After centrifugation, the blood is separated into three layers;
o   A tall bottom layer of packed red cells.

o   A very thin middle layer of WBC and platelets (the ‘buffy layer’)

o   The top layer of clear plasma.

  • The percentage of the height of red cell volume constitutes the packed cell volume or hematocrit.

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