Final answer:
The preferred anticoagulant for preparing blood films for a manual differential leukocyte count is EDTA, as it preserves cell morphology and prevents clotting. This allows for proper staining and visualization of leukocytes to perform the count.
Step-by-step explanation:
The specimen of choice for preparation of blood films for manual differential leukocyte count is whole blood collected in EDTA (ethylenediaminetetraacetic acid). EDTA is a commonly used anticoagulant in hematology because it preserves the shape of blood cells and prevents clotting by binding to calcium in the blood. The use of K2EDTA as an anticoagulant allows for the preparation of blood smears that are stained using methods such as Wright-Giemsa stain, providing clear differentiation of the leukocyte types.
Once whole blood is drawn into an EDTA tube, it can be carefully spread onto a microscope slide to create a thin layer referred to as a blood smear. This smear is then stained to allow for the visualization of the different types of leukocytes. A manual count is carried out by scanning the smear systematically and identifying and classifying at least 50 to 100 cells to determine if the percentages of cell types are within normal ranges or indicate an abnormality such as leukocytosis, which is often an expected finding in cases of infection or inflammation.