What tool is used to count white blood cells manually?

The hemacytometer is specifically designed for counting cells, including white blood cells, manually. It consists of a specialized glass slide with a grid pattern etched into it, which allows for accurate cell counting under a microscope. Technicians use it by placing a small volume of diluted blood into the hemacytometer, which helps count the number of white blood cells in a specified volume, providing valuable information about a patient's immune status and overall health.

The microscope plays an essential role in visualizing the cells counted with the hemacytometer but is not a counting tool itself. A spectrophotometer is used for measuring light absorbance or transmittance in a solution, which does not apply to cell counting. Lastly, a hemoglobinometer is designed specifically for measuring hemoglobin concentration in blood, which is unrelated to white blood cell counting. Each of these tools has its unique purpose, but for the manual counting of white blood cells, the hemacytometer is the correct choice.