4 During pregnancy, there is a gradual increase in the normal WBC count (third trimester 95% upper limit = 13,200 per mm 3 and 99% upper limit = 15,900 per mm 3 ), and a slight shift toward an increased percentage of neutrophils. 3 There is also a shift from relative lymphocyte to neutrophil predominance from early childhood to the teenage years and adulthood. By two weeks of age, this decreases to approximately 5,000 to 20,000 per mm 3 (5.0 to 20.0 × 10 9 per L), and gradually declines throughout childhood to reach adult levels of 4,500 to 11,000 per mm 3 (4.5 to 11.0 × 10 9 per L 95% confidence interval) by about 21 years of age. 3 Healthy newborn infants may have a WBC count from 13,000 to 38,000 per mm 3 (13.0 to 38.0 × 10 9 per L) at 12 hours of life (95% confidence interval). The normal range for WBC counts changes with age and pregnancy ( Table 1). If malignancy cannot be excluded or another more likely cause is not suspected, referral to a hematologist/oncologist is indicated. Symptoms suggestive of a hematologic malignancy include fever, weight loss, bruising, or fatigue. Other nonmalignant etiologies of leukocytosis include certain medications, asplenia, smoking, obesity, and chronic inflammatory conditions. Stressors capable of causing an acute leukocytosis include surgery, exercise, trauma, and emotional stress. The peripheral white blood cell count can double within hours after certain stimuli because of the large bone marrow storage and intravascularly marginated pools of neutrophils. Leukocytosis is a common sign of infection, particularly bacterial, and should prompt physicians to identify other signs and symptoms of infection. The leukocyte differential may show eosinophilia in parasitic or allergic conditions, or it may reveal lymphocytosis in childhood viral illnesses. A repeat complete blood count with peripheral smear may provide helpful information, such as types and maturity of white blood cells, uniformity of white blood cells, and toxic granulations. It is important to use age- and pregnancy-specific normal ranges for the white blood cell count. An elevated white blood cell count has many potential etiologies, including malignant and nonmalignant causes.
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