Blood Differential

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Why is the Test Performed?

The differential count can be used to help detect infection, anemia, and leukemia or to follow the progress of treatment.

There are various types of WBCs (also called leukocytes) that normally appear in the blood. The differential determines the relative percentages of the different types of cells in the blood, notes any abnormal appearance of the cells, and the presence of any abnormal immature cells.

• Neutrophils are mainly phagocytic cells (that is, they engulf and destroy invading organisms). They also release some enzymes and substances that affect the function of other cells called cytokines.
• B lymphocytes (B cells) synthesize and secrete antibodies.
• T lymphocytes (T cells) -- one type of T cell is called a helper cell; it secretes proteins that increase B cell function and the functions of cytotoxic T lymphocytes. Cytotoxic T lymphocytes recognize and destroy virus-infected and other abnormal cells.
• Monocytes recognize a variety of microorganisms, especially gram-negative bacteria. Activated monocytes turn into macrophages that can engulf and destroy microorganisms and secrete a variety of cytokines that modulate the activity of other leukocytes.
• Eosinophils and basophils release substances that cause vasoconstriction, smooth muscle contraction, and an increased permeability of small blood vessels. Eosinophils are stimulated by parasites and some bacteria. Basophils are stimulated by allergens.