To determine the packed cell volume of the given sample of blood.

PRINCIPLE: When a known volume of blood is centrifuged, the cells being heavier, settle down leaving a clear

column of plasma above.

APPARATUS: Wintrobe’s hematocrit tube, syringe (Pasteur pipette) with a long polythene tube attached to the nozzle, Centrifuge, oxalated venous blood, sterile needle, spirit, cotton.

Wintrobe’s tube is a glass tube one end of which is closed. It is 11 cms long and internal diameter of 3 mm and graduated from Oto lOin both directions. It contains 1 ml. of blood. Venous blood is anticoagulated by treating with double oxalate mixture containing ammonium oxalate and potassium oxalate in the ratio 3:2. (2 mgI ml of blood is used). Oxalated blood is used as it will not alter the morphology of the cell. Ammonium oxalate produces swelling of RBC and potassium oxalate produces shrinkage of RBC. Their actions are counterbalanced. Here we use venous blood with CPD-A solution.

PROCEDURE: Anti coagulated blood is taken in the Pasteur pipette without any air bubble. Introduce the tip of the polythene tube into the haematocrit tube, till it reaches the bottom without any air bubble. Fill up to the top zero mark and wipe off any blood sticking to the sides of the tube. The mouth of the tube is closed with a cotton plug to prevent fluid evaporation. Then it is centrifuged for 30 minutes at a speed of 3000 revolutions/minute. The height of the column of packed cells is directly read from the haematocrit tube and expressed as percentage.


The red cells are seen packed at the bottom and straw coloured column of plasma is seen above that. In between there is a greyish white layer consisting of WBC5 and platelets. This layer is “buffy coat” and is 0.5-1 mm in thickness.


P.C.V. is the relative volume of cells to plasma and expressed as percentage of whole blood.

Normal values: Male: 47 +1- 7%, Female: 42 +/- 7%


a. High P.C.V. is seen physiologically in:

1. Newborns 2. High altitudes 3. After exercise

4. Dehydration resulting from profuse sweating without adequate fluid intake.

Pathologically in:

1. Polycythemia

2. Dehydration resulting from severe gastroenteritis

3. Burns leading to haemoconcentration.

b. Low P.C.V. is seen physiologically in: Pregnancy (due to haemodilution) Pathological conditions: In various types of anaem ias.

Plasma column: It is normally straw coloured. Reddish tinge indicates hemolysis. It is yellow in jaundice, milky and opaque in lipaemia.

Buffy coat: Thickness of buffy coat gives a rough idea of leucocyte count. In leukemias, the thickness is increased.


Draw and label Wintrobe’s haematocrit tube. What are it’s uses?

What are the sources of error in the measurement and interpretation of PCV?








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