When a newborn is born, the total leukocyte count is very high, with a value of (15-20) × 10^9/L. It gradually rises within 24 hours after birth, peaking at about 25 × 10^9/L at 24 hours, and then gradually declines, with an average leukocyte count of 12 × 10^9/L after two weeks, which is usually higher than that of adults. The increase is due to the infant’s ability to increase its resistance to the outside world by raising its white blood cells as it transitions from the mother’s womb to the outside world. In addition, intense crying, feeding, muscle tension, and hypoxia in newborns can also cause a physiological increase in leukocytes. In addition to physiological increase, neonatal leukocyte increase can also be caused by disease factors, which parents should pay attention to. The most common clinical factor is infection, usually caused by bacterial infection, such as intrauterine infection, umbilical cord infection, lung infection, etc. In severe cases, there are systemic infectious diseases, including sepsis, septic meningitis, etc., which are accompanied by corresponding clinical symptoms, such as nasal congestion, runny nose, cough, poor feeding, poor response, fever, jaundice receding and reappearing, etc., which require timely anti-infection treatment. In addition, neonatal post-surgery and trauma may also be associated with elevated white blood cells; neonatal hematologic disorders, such as leukemia, may also lead to an increase in white blood cells, requiring prompt medical attention and corresponding treatment.