White blood cells are the body cells that are responsible for fighting infectious agents. They circulate at low levels in the blood stream, and rapidly appear when a foreign invader is detected. The breakdown of types of white blood cells depends on age and type of infection, but in general all white cells together should number between 9 and 34 billion cells per liter of blood in a healthy newborn immediately after birth.
White blood cells are counted to determine whether a patient has an infection or a disorder of white blood cell production. White blood cell count is a part of a standard complete blood count. When counted, both the total number and breakdown of types of white cells are counted. In the case of an abnormal number, a physician can identify potential diagnoses from the type of cell that has an abnormal number.
A newborn has an extremely elevated white blood cell number immediately after birth. According to normal numbers that have been established at the Children's Hospital of Buffalo, total white cell number in the month after birth should be between 9 and 34 billion white blood cells per liter of blood. This number begins to fall drastically during the first two years of life, when normal levels are between 6 and 14 billion white blood cells per liter of blood.
White blood cells consist of lymphocytes, neutrophils, monocytes, eosinophils and basophils. Each of these have normal ranges within the total count. In newborns, the total number of lymphocytes and neutrophils can be greatly expanded. In fact, during infancy and into school age years, it is typical for children to have lymphocyte counts that exceed neutrophil counts. This characteristic will reverse before the child reaches adulthood.
Changes in White Blood Cell Count
The most common reason for white blood cell counts to change is infection. Bacterial, viral, fungal and parasitic infections each cause characteristic changes to white blood cell number. Additionally, white blood cell counts can increase for benign reasons, such as exercise or stress, or more dangerous conditions, such as leukemia. Low white blood cell counts can also mean infection, or they can be a normal result of the birthing process.
Immediately after birth, white blood cell count is part of the standard screening tests for your newborn. The physicians will monitor blood cell counts closely in at-risk newborns. Drastic changes in white blood cell count could indicate the need for intervention, but due to the variable range of normal white blood cell counts in newborns, additional testing will likely be necessary.