A healthy adult human has between 4,500 and 11,000 white blood cells per cubic millimeter of blood. Fluctuations in white cell number occur during the day; lower values are obtained during rest and higher values during exercise. An abnormal increase in the number of white cells is known as leukocytosis, whereas an abnormal decrease in number is known as leukopenia. White cell count may increase in response to intense physical exertion, convulsions, acute emotional reactions, pain, pregnancy, labour, and certain disease states, such as infections and intoxications. The count may decrease in response to certain types of infections or drugs or in association with certain conditions, such as chronic anemia, malnutrition, or anaphylaxis. In general, newborns have a high white blood cell count that gradually falls to the adult level during childhood.
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