Question

A 1:20 dilution is made for a manual WBC count. The four corner squares on both sides of a hemocytometer are counted. A total of 100 cells are counted (eight total squares). What is the white blood cell count in terms of a liter?

a. 2.5×10^9/L
b. 25×10^9/L
c. 2500/L
d. 25,000/L

Answer 1

After counting 100 WBCs in 0.8 microliters of a diluted sample and calculation, the WBC count per liter is found to be 2.5×10^9 cells/L.

Step-by-step explanation:

To calculate the white blood cell count (WBC) per liter from a 1:20 dilution, first consider that 100 cells were counted in eight squares of the hemocytometer. This means that in each square, there were on average 12.5 cells (100 cells ÷ 8 squares).

The volume that corresponds to one square of the hemocytometer is typically 0.1 μL.

Since we have the count from eight squares representing 0.8 μL, we'll multiply the average count per square by the reciprocal of this volume to scale it up to 1µL, and then we can use the dilution factor to find the concentration in the original solution.

To find the count per microliter (μL), divide 100 cells by 0.8 μL to obtain 125.

Then, considering the dilution factor (1:20), to find the count in the original sample per μL, multiply 125 by 20 to get 2500 cells/μL.

WBC counts are usually given per liter, so to convert to cells per liter, multiply 2500 cells/μL by the conversion factor of 106 μL/L to obtain 2.5×109 cells/L.

This is the WBC count in terms of a liter.