7. Switch to the high-power lens and count the number of cells in field 1. Move the hemacytometer until field 2 is in focus and repeat the counting procedure. Continue until the cells in all five fields have been counted. Note that the fields are numbered clockwise around the chamber, with field 5 being in the center. Count the fields in this order. To count the cells in each field, start in the upper left small square and follow the pattern indicated by the arrow in figure 6-8. Count all of the cells within each square, including cells touching the lines at the top and on the left. DO NOT COUNT ANY OF THE CELLS TOUCHING THE LINES ON THE RIGHT AND AT THE BOTTOM.
8. Total the number of cells counted in all five fields and multiply by 10,000 to arrive at the number of red cells per cubic millimeter of blood. The number of cells counted in each field should not vary by more than 20. A greater variation may indicate poor distribution of the cells in the fluid, resulting in an inaccurate count.
9. Immediately after completing the count, clean the counting chambers 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.
Some common sources of error are:
Uniopette Method
The Uniopette disposable diluting pipette system for the red blood cell count provides a convenient, precise, and accurate method for obtaining a red blood cell count. The disposable kit consists of a shielded capillary pipette (10 microliter (ul) capacity) and a plastic reservoir containing a premeasured volume of diluent (1:200 dilution).
Procedure
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 blood collection stops automatically, e.g., when the proper amount (10 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 the index finger and seat the capillary tube holder in the reservoir neck. Release pressure on the reservoir and remove the finger from the overflow chamber opening. Suction will draw the blood into the diluent in the reservoir.
4. Squeeze the reservoir gently two or three times to rinse the capillary tube, forcing diluent into—but not out of—the 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 the 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.