leukocytosis of the newborn

leu·ko·cy·to·sis of the new·born

an apparently "physiologic" leukocytosis usually observed in newborn infants, in whom the white blood cell counts usually exceed 10,000/mm3, and sometimes range to 45,000/mm3, resulting chiefly from increased numbers of neutrophils (especially single and bilobed forms). On the third or fourth day of life, the count generally decreases rapidly, and then fluctuates for several days; beginning about the fourth week of life, a relative lymphocytosis is observed, and this normally continues for a few years.
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