6. When all the cells in the four fields have been counted, multiply the count by 50 for the total white cell count.
7. Immediately after completing the count, clean the counting chamber with distilled water and dry it with lens tissue. Rinse pipettes first with cold water, then with acetone. Draw air through the pipette until it is dry. The pellet should move freely in the bulb if the pipette is dry.
Sources of error. The errors are generally caused by the same mistakes as described for red cell counts.
The Uniopette disposable kit for doing a white blood cell count consists of a shielded capillary pipette (20 ul capacity) and a plastic reservoir containing a premeasured volume of diluent (1:100 dilution).
1. Using the shield on the capillary pipette, puncture the diaphragm in the neck of the reservoir with the tip of the capillary shield.
2. After obtaining free-flowing blood from a lancet puncture of the finger, remove the protective plastic shield from the capillary. Holding the capillary slightly above the horizontal, touch the tip to the blood source. Capillary action will fill the tube until the blood collection stops automatically, e.g., when the proper amount (20 ul) has been obtained. Wipe blood off the outside of the capillary tube, making sure none is removed from inside the capillary tube. An alternative source of blood is a thoroughly mixed fresh venous blood sample obtained by venipuncture.
3. Squeezing the reservoir slightly, cover the upper opening of the capillary overflow chamber with your index finger and seat the capillary tube holder in the reservoir neck. Release pressure on the reservoir and remove your finger from the overflow chamber opening. Suction will draw blood into the diluent in the reservoir.
4. Squeeze the reservoir gently two or three times to rinse the capillary tube, forcing diluent intobut not out ofthe overflow chamber, releasing pressure each time to return diluent to the reservoir. Close the upper opening with your index finger and invert the unit several times to mix the blood sample and diluent.
5. For specimen storage, cover the overflow chamber of the capillary tube with the capillary shield.
6. Immediately prior to cell counting, mix adequately again by gentle inversion, taking care to cover the hole with your index finger.
7. Remove the pipette from the reservoir. Squeeze the reservoir and reseat the pipette in the reverse position, releasing pressure to draw any fluid in the capillary tube into the reservoir. Invert and fill the capillary tube by gentle pressure on the reservoir. After discarding the first 3 drops, charge the counting chamber of the hemacytometer by gently squeezing the reservoir.
8. Using the high power objective, count the white blood cells in the nine large squares of the hemacytometer chamber.
9. Calculation: Add 10 percent to the number of cells counted in the nine large squares and multiply by 100 to obtain the white cell count.
Example: The number of cells in 9 large squares was 90.
The cell count = [90 + (0.1 x 90)] x 100
= [ 90 + 9 ] x 100
= 99 x 100= 9900
The total white cell count is not necessarily indicative of the severity of a disease, since some serious ailments may show a low white cell count. However, the percentage distribution of the different types of leukocytes in the blood often provides more helpful information in determining the severity and extent of the infection than any other single procedure used in the examination of the blood. The differential count gives these percentages.