For determination of the white cell count, 0.025 ml of blood was diluted to 0.50

Question

For determination of the white cell count, 0.025 ml of blood was diluted to 0.50 ml (1:20 dilution). After diluting the blood sample and mixing, the hemacytometer chamber was loaded. An average count of 25 white cells were observed in one "W" section of the hemacytometer. The area of a "W" section on the grid is 1.0 mm2. The distance between the coverglass and the ruled area is 0.1 mm. Calculate the number of white cells (leukocytes) in 1 cubic mm of blood.

A. 25/cubic mm

B. 2.5/cubic mm.

C. 500/cubic mm

D. 5,000/cubic mm.

Explanation / Answer

The correct option is D that is 5000/cubic mm.

Here the area of "W" 1.0 mm2 which contains 25 white blood cells. Area includes only width X length, hieght is not included in area, but here we have to determine the number of cells in 1 cubic mm which is unit of volume. Thus, to convert area into volume, multiplication with hieght (0.1mm) is required.

Thus total volume = 1 mm2 X 0.1mm = 0.1 mm3 or 0.1 cubic mm. Since total number in 0.1 cubic mm = 25 therefore total number of cells in 1 cubic mm = 25 X 10 =250.

But here, the blood has been diluted by 1:20 ratio therefore total number of cells in 1 cubic mm will be 250 X 20 = 5000.

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