Final answer:
A differential white blood cell count ("diff") identifies the percentage of various types of white blood cells, which are pivotal for the immune system. It involves counting and classifying WBCs in a stained blood smear, and deviations from normal ranges help diagnose health issues.
Step-by-step explanation:
A differential white blood cell count ("diff") determines the percentages of each type of white blood cells (WBC). White blood cells are a critical component of the immune system, defending the body against infections and diseases. They are identified by their distinct morphology, which includes having a nucleus and lacking hemoglobin, unlike red blood cells. A diff count involves creating a blood smear, which is stained with Wright-Giemsa stain to highlight the cells and their features. Under a microscope, the technologist tallies the different types of WBCs, such as granulocytes (neutrophils, eosinophils, and basophils) and agranulocytes (lymphocytes and monocytes), until 100 cells are counted. The percentage of each WBC type is calculated to help diagnose and monitor various health conditions. The typical concentration of WBCs in blood is about 1,000 to 11,000 per microliter, and deviations from normal range may indicate the presence of disease.