What is the formula used to calculate cell concentration from a blood sample?

The formula for calculating cell concentration from a blood sample is accurately expressed in the second choice. It considers the total number of cells counted along with the dilution factor, which is essential when samples have been diluted to achieve a count that's manageable and accurate under a microscope.

In this formula, the total cells counted refers to the actual number of cells observed during the counting process. The dilution factor accounts for the proportion of the original sample being counted compared to the diluted sample used. It ensures that the final concentration reflects the actual amount of cells in the original undiluted sample.

The division by the number of squares counted is also crucial. When using a counting chamber, such as a hemacytometer, the observer counts cells within specific square areas defined on the chamber. Since the total volume analyzed is limited to only a fraction of the entire sample volume, the formula incorporates the number of squares counted to extrapolate the total concentration per milliliter.

Using this formula allows for accurate adjustments based on the dilution and specific area counted, thereby yielding a reliable concentration of cells in the original blood sample.