Diagnostic Laboratory Section

WINTROBE METHOD

• Blood is filled up to 10 mark in the Wintrobe tube using Wintrobe pipette, avoiding air bubbles. Keeping the tip of the pipette below the level of blood while filling, avoids air bubbles.

• The tube is centrifuged at 3000 to 4000 rpm for 45 to 60 minutes. The level of RBC column below the buffy coat is read and express the PCV in percentage.

Buffy coat

• It represents leucocytes. Normal animal have a buffy coat of 0.5 to 1.2 mm. Up to 1 mm of buffy coat each 0.1 mm corresponds to 1000 WBC and for every 0.1 mm above 1 mm it is equivalent to 2000 WBC.
• Buffy coat of 2 mm or more indicates leucocytosis or in excess, leukaemia. However this should never be used as a substitute for total WBC count.

Trapped plasma

• In the haematocrit, plasma, WBC and platelets get trapped between the red cells. This trapped plasma increases the PCV which depends on the number of cells in rouleaux formation and the size of the RBC.
• Dog with large red cells and horse blood with more rouleaux formation have less trapped plasma. The correction factor for trapped plasma of 5 per cent for dog and horse and 6 per cent for bovine has to be deducted from PCV value in Wintrobe method.

Microhaematocrit method

• A 7 cm long capillary tube with a bore of 1 mm is charged with oxalated blood up to ¾ of its length. When blood sample is directly taken into the tube, a heparinised tube should be used.
• Blood on the outside of the tube is wiped off and the vacant end of the tube is sealed with special clay or by holding it in the flame.
• This is placed in the slot provided in the special micro haematocrit centrifuge and rotated at 12,000 rpm for 2 min. The column of packed RBC is read using special reader for determining the percent of red blood cell.
• Microhaematocrit prevents trapped plasma interference, requires less time and is more accurate than Wintrobe method.