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Medical Definition of Leukocytosis of the newborn
1. An apparently "physiologic" leukocytosis usually observed in newborn infants, in whom the white blood cell counts are usually greater than 10,000 per cu mm, and sometimes range to 45,000 per cu mm, 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. (05 Mar 2000)