Hemacytometer

    

     Cell counts are performed manually by diluting blood with a diluent, loading a small amount of the diluted sample on a ruled device (hemacytometer), and counting the cells microscopically. The hemacytometer consists of two side-by-side identically ruled glass platforms mounted in a glass holder. Each platform contains a ruled square measuring 3 X 3 mm (9 mm²) and is subdivided according to the improved Neubauer ruling. This ruling subdivides the ruled square into 9 large squares, each measuring 1 X 1 mm (1mm²). All 9 squares are used for leukocyte counts. The large center square is used for platelet and erythrocyte counts. This center square is divided into 25 smaller squares, each with an area of 0.04 mm². The 5 squares labeled R are used in performing the erythrocyte count whereas the entire center square is used in performing the platelet count.

     On either side of the two ruled glass platforms is a raised ridge. The coverglass is placed on top of the ridge. The distance between the coverglass and the surface of the ruled
area (depth) is exactly 0.1 mm. Thus, the ruled area on each side of the hemacytometer holds a volume of 0.9 mm³ (3 X 3 X 0.1).

     The unopette system is a fast and accurate method for collecting and diluting blood for cell counts. For each laboratory determination performed, the unopette consists of the following elements: the reservoir, the pipet, and the pipet shield. The reservoir contains a premeasured volume of diluting fluid that is specific for the cell count to be performed.

Figure: Unopette system (from left to right): pipet shield, pipet, and reservoir. 

     In summary: 

Figure: Neubauer hemacytometer counting area. The entire counting area is 9 mm² (3 mm × 3 mm) and is divided into 9 squares. Each square is 1 mm² (1 mm × 1 mm) in area. Using the 10× objective, 1 square of the counting area (1 mm²) can be viewed. For the manual leukocyte count, all 9 squares are counted. The center square is further divided and the R squares are used for erythrocyte counts, while the entire center square is used for platelet counts.