What is the procedure called when a blood smear is stained and the number of leukocyte types is counted?

The procedure where a blood smear is stained and the types of leukocytes (white blood cells) are counted is known as a differential leukocyte count. This process typically involves using Wright's stain, which is specifically designed for staining blood cells to enable the visualization of different leukocyte types under a microscope.

Wright's stain works by providing contrast to various cellular components and allowing the identification of different white blood cells, such as neutrophils, lymphocytes, monocytes, eosinophils, and basophils. This staining technique is crucial in hematology for diagnosing conditions like infections, allergies, and blood disorders.

In contrast, options like Gram staining are primarily used to categorize bacteria into gram-positive and gram-negative types based on the characteristics of their cell walls. Sudan staining is used for detecting lipids, and hematoxylin staining is often employed in histology for cell and tissue structure visualization but not specifically for blood smears. Thus, the choice of Wright's stain is appropriate for the procedure described in the question.