Final answer:
A differential white blood count estimates the proportions of different types of white blood cells in the blood, providing important information on a patient's health condition, such as the presence of infection or other abnormalities compared to standard references.
Step-by-step explanation:
A testing of differential white blood count is performed to estimate the proportion of different types of white blood cells (WBCs or leukocytes) in the blood. This test plays a crucial role in detecting the presence of infections or other health conditions. It involves making a blood smear, staining it with Wright-Giemsa stain, and examining it to determine the relative percentages of each type of WBC. Clinically, this can reveal conditions like neutrophilia, which suggests an infection if there is a raised white cell count. The results are compared against normal ranges that vary according to age and gender, usually between 3.5 to 11 x 10⁹ cells/L.
Each white blood cell type is associated with different disease conditions when their numbers increase or decrease. For instance, a differential might indicate the presence of high blood calcium levels (hypercalcaemia) or check renal function. The count is performed by scanning the smear in a pattern that ensures unique counts for each cell and determining percentages after observing 100 cells. The count gives an insight into a patient's overall state of health by comparing it to normal values and identifying any anomalies.