INTRODUCTION
There are 2 main techniques in order to perform a differential white cell count:

• Manual method = The battlement technique.
• Cell counter = The improved Nebauer Haemocytometer.

Battlement Technique

1. Put on your lab coat and ensure that long hair is tied back and any jewellery removed.
2. Ensure that you have a flat, clean, dry surface upon which to work.
3. Check the microscope for safety, ie the plug and electrical cable.
4. Scan the film under low power noting:
   • Film quality.
   • Stain quality.
   • Cell numbers.
5. Scan the far end of the film for platelet clumps and any large abnormal cells, remember that white cells are heavier than the red cells and are therefore swept to the tail of a smear.
6. Select an area of the film approximately one third from the end of the slide for examination under oil immersion.
7. Use the battlement technique as follows:
   • Move 2 fields along the edge, 2 fields up, 2 along and then 2 down.
   • Continue until 100 cells have been counted.
   • Record numbers of each type of cell.
   • Express as absolute numbers or as a percentage of the total white blood cells.
   • Remember that red blood cells are also present; these should also be observed and commented upon.

Improved Neubauer Haemocytometer Method

1. Put on your lab coat and ensure that long hair is tied back and any jewellery removed.
2. Ensure that you have a flat, clean, dry surface to work upon.
3. Dilute the blood:
   • Use a 2ml automatic pipette to withdraw 2mls of white blood cell diluting fluid (Tork - phosphate buffered saline, acetic acid, gentian violet) into a small test tube.
   • Add 100ul of blood from a well mixed EDTA sample; depress the plunger several times to mix the solution.
4. Fill the counting chamber:
   • Ensure counting chamber and cover slip are clean and dry.
   • Apply the cover slip (Newton's rings should be visible - small rainbow circles along the edges).
   • Fill a capillary tube with the diluted blood and place a finger over the top.
   • Transfer the tube to the counting chamber.
   • Hold the capillary tube at a 45 degree angle to the cover slip and allow a small amount of fluid to be drawn inside (there should be no bubbles and no fluid in the grooves upon either side of the chamber); both sides of the chamber should be filled.
5. Check the microscope for safety, ie the plug and electrical cable.
6. Count the cells.
   • Keep the chamber horizontal and transfer it to the stage of the microscope.
   • Count the cells in the 4 large squares located on the outside using the 40 x objective.
7. The calculation is as follows:
   
   NUMBER OF CELLS IN 4 SQUARES DIVIDED BY 20 = WBCS x 10 to the power of 9/L