Question

Your sample will now be diluted to 1:2000 with an isotonic saline solution. Furthermore, when using a hemocytometer to count RBCs, only five squares of the central field are counted as indicated by the following diagram

by the following diagram: 400X 100X Figure 4: Pattern used for counting RBCs in the center field of a hemocytometer. Upon loading your diluted sample into the hemocytometer, these 5 squares are observed:

(Total # of cells counted)(10/# of 1 mm^2 fields counted)(dilution factor) = # of cells/ul

Answer 1

We need to find the RBC concentration of a blood sample using a hemocytometer. We count the number of RBCs in 5 out of 25 squares in the central grid of the hemocytometer.

The number of cells in each of the five square is :

Square 1: 55

Square 2: 42

Square 3: 48

Square 4: 57

Square 5: 55

Total number of RBCs in the five squares = 55 + 42 + 48 + 57 + 55 = 257.

Total RBC count = N * Dilution / Area* depth

where N is the number of cells counted in the 5 squares

The volume of sample is given by the product of the area and the depth of the hemocytometer. The depth is 0.1 mm (the space between the grooved area of the hemocytometer and the cover slip).

The dilution used here is 1/2000, so the dilution factor is 2000.

Given, the area of central grid with 25 squares as 1 mm². and also it is mentioned that the five cells account for an area that is 1/5^th of the central grid. which means we have covered only 1/5 th of the area of 1 mm². Therefore, area would be 1* 1/5 = 1/5.

Total RBC count (cells/ mm³) = 257* 2000 / 1/5* 0.1 = 514000 / 0.02 = 25700000 = 2.5* 10⁷.

Therefore, the number of RBCs in the original sample is 2.5* 10⁷ cells / mm³ or 2.5* 10⁷ cells / uL (1 mm³ = 0.001 mL = 1 uL).