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Blood films are made by placing a drop of blood on one end of a slide, and using a spreader slide to disperse the blood over the slide's length. The aim is to get a region, called a monolayer, where the cells are spaced far enough apart to be counted and differentiated. The monolayer is found in the "feathered edge" created by the spreader slide as it draws the blood forward.
The slide is left to air dry, after which the blood is fixed to the slide by immersing it briefly in methanol. The fixative is essential for good staining and presentation of cellular detail. After fixation, the slide is stained to distinguish the cells from each other.
Routine analysis of blood in medical laboratories is usually performed on blood films stained with Romanowsky, Wright's, or Giemsa stain. Wright-Giemsa combination stain is also a popular choice. These stains allow for the detection of white blood cell, red blood cell, and platelet abnormalities. Hematopathologists often use other specialized stains to aid in the differential diagnosis of blood disorders.
After staining, the monolayer is viewed under a microscope using magnification up to 1000x. Individual cells are examined and their morphology is characterized and recorded.
(2) To monitor the effect of chemotherapy and radiotherapy on bone marrow.
(3) To provide direction for further investigations that will help in arriving at the correct diagnosis (e.g. in infections, drug toxicity, etc.). Blood smear examination is therefore indicated in clinically suspected cases of anemia, thrombocytopenia, hematological malignancies (leukemia, lymphoma, multiple myeloma), disseminated intravascular coagulation, parasitic infections (like malaria or filaria), infectious mononucleosis, and various inflammatory, or malignant diseases.