White Blood Cell Count and Dif... Health Article

KEY TERMS

Band cell—An immature neutrophil at the stage just preceding a mature cell. The nucleus of a band cell is unsegmented.

Basophil—Segmented white blood cell with large dark blue-black granules that releases histamine in allergic reactions.

Differential—Blood test that determines the percentage of each type of white blood cell in a person's blood.

Eosinophil—Segmented white blood cell with large orange-red granules that increases in response to parasitic infections and allergic reactions.

Lymphocyte—Mononuclear white blood cell that is responsible for humoral (antibody mediated) and cell mediated immunity.

Monocyte—Mononuclear phagocytic white blood cell that removes debris and microorganisms by phagocytosis and processes antigens for recognition by immune lymphocytes.

Neutrophil—Segmented white blood cell normally comprising 50-70% of the total. The cytoplasm contains both primary and secondary granules that take up both acidic and basic dyes of the Wright stain. Neutrophils remove and kill bacteria by phagocytosis.

Phagocytosis—A process by which a white blood cell envelopes and digests debris and microorganisms to remove them from the blood.

• Lymphocytes are the second most abundant WBCs. They may be small (7-9 μm in diameter) or large (12-16 μm in diameter). The nucleus is dark blue and is nearly round or slightly indented and the chromatin is clumped and very dense. The cytoplasm is medium blue and usually agranular. An occasional lymphocyte will have a few azurophilic granules in the cytoplasm. Lymphocytes originate in the lymphoid tissues and are not phagocytic. They are responsible for initiating and regulating the immune response by the production of antibodies and cytokines.
• Monocytes are the largest WBCs measuring 14-20 μm in diameter. They have a large irregularly shaped and folded blue nucleus with chromatin that is less dense than other WBCs. The cytoplasm is grey-blue, and is filled with fine dust-like lilac colored granules. Monocytes are phagocytic cells that process and present antigens to lymphocytes, an event required for lymphocyte activation.

Preparation

This test requires a 3.5 mL sample of blood. Venipuncture is usually performed by a nurse or phlebotomist following standard precautions for the prevention of transmission of bloodborne pathogens. There is no restriction on diet or physical activity.

Aftercare

Discomfort or bruising may occur at the puncture site. Pressure to the puncture site until the bleeding stops reduces bruising; warm packs relieve discomfort. Some people feel dizzy or faint after blood has been drawn and should be treated accordingly.