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During many kinds of bacterial infections there is an increase in the total number of white blood cells (WBC). The increase is called leukocytosis. Diseases that can cause the increase include appendicitis, meningitis, bacterial pneumonia, etc. Some bacterial infections result in a decrease of WBC, which is referred to as leukopenia. Leukopenia is associated with diseases such as typhoid fever, tuberculosis, etc. Some viral diseases such as measles and influenza may also cause a leukopenia.
White blood cell (WBC, or leukocytes) and red blood cell (RBC, or erythrocytes) counts are done by diluting a blood sample and counting the number of cells present using a microscope. The blood plasma contains a number of different types of WBC. The different types of WBC and their percentages can be determined by doing a differential count on a blood smear, which has been stained with Wright's or Giemsa stain. The percentages of different WBC and their functions are shown below.
Type of cell Number/cubic mm Function
RBC (Erythrocytes) 4.5-5.5 million Transport O 2 & CO 2
WBC (leukocytes) 5-10 thousand combat infection, phagocytose
A. Neutrophils (PMNs) / (60-70%) / phagocytic
B. Eosinophils / (2-4%) / phagocytic - increase during allergic reactions
C. Basophils / (0.5-1%) / release heparin & histamine
A. Lymphocytes / (20-30%) / humoral and cell-mediated immune responses
B. Monocytes / (3-8%) / phagocytic upon maturing into macrophage
A good way to remember the relative proportions of WBC’s is … Never Let Monkeys Eat Bananas (Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils).
*Note –In addition to cells, one may also note small “cell-like” constituents called platelets. These small constituents are important for clotting.