Final answer:
A differential count is used to determine the percentage of each type of white blood cell on a stained blood smear by scanning and tallying 100 cells after staining, often with Wright-Giemsa stain, to identify the percentage of different leukocytes.
Step-by-step explanation:
The type of white blood cell count that is used to determine the percentage of each type of white blood cell seen on a stained blood smear is called a differential count. When performing a differential count, a blood smear is first stained, often with Wright-Giemsa stain, and examined under a microscope. The technologist scans the slide using a systematic pattern to prevent counting the same cells more than once. As white blood cells are identified, they are recorded in a tally until a total of 100 cells is reached. By dividing the number of each type of cell by the total number of cells (usually 100), the percentage of each cell type present is ascertained.
To ensure a thorough evaluation, the technologist needs to recognize and differentiate the various formed elements within the blood smear such as leukocytes, erythrocytes, and thrombocytes. A common method for organizing this process is by constructing a simple table for the leukocyte types and making a mark for each identified cell. This process helps in determining whether the percentages observed are within the normal range or if there is an indication of an abnormality in the blood smear.