Final answer:
A differential cell count measures the different types of white blood cells but does not determine the number of red blood cells, which requires a complete blood count.
Step-by-step explanation:
A differential cell count is a technique used to measure and analyze the different types of white blood cells in a blood sample. This test determines each of the following EXCEPT the: C. number of red blood cells. A differential cell count is leveraged for its ability to determine the total number of white blood cells (leukocytes), the numbers of each type of white blood cells (such as lymphocytes, monocytes, neutrophils, eosinophils, and basophils), and can sometimes hint at the presence of cancer through the identification of abnormal cells or levels of specific cell types. However, it does not provide information on the number of red blood cells (erythrocytes), as this is typically assessed with a different set of tests like the complete blood count (CBC).
To achieve accurate results in a differential cell count, blood smears are stained with Wright-Giemsa stain and then examined under a microscope. Each white blood cell observed is identified by its cell type and included in a tally until 100 cells have been counted, from which the relative percentages of each cell type are calculated. This allows for the determination of both the overall number and the relative proportions of white blood cells.