Chapter 126 Leukocytosis
Leukocytosis is an elevation in the total leukocyte, or white blood cell (WBC), count that is 2 standard deviations above the mean count for a particular age (Chapter 708). The various causes of leukocytosis are categorized by the class of leukocyte that is elevated and whether the process is acute, chronic, or lifelong. To evaluate the patient with leukocytosis, it is critical to determine which class of WBCs is elevated, and also the duration and extent of the leukocytosis. Each blood count should be evaluated with regard to the absolute number of cells/µL and the normal range for the patient’s age.
A >5% proportion of immature neutrophil cells is termed a left shift and indicates rapid release of cells from the bone marrow. This release may result in increased circulating band forms, which usually constitute 1-5% of circulating neutrophilic cells, or metamyelocytes and myelocytes, which are not usually found in the peripheral circulation. Higher degrees of left shift with more immature neutrophil precursors are indicative of serious bacterial infections but may also be encountered with trauma, burns, surgery, acute hemolysis, or hemorrhage.
Neutrophilia
Neutrophilia is an increase in the total number of blood neutrophils, which for older children and adults is >8,000/µL. During the 1st day of life, the upper limit of the normal neutrophil count ranges from 7,000 to 12,000/µL. In the 1st mo of life, the neutrophil count ranges from 1,800 to 5,400/µL, and by 1 yr of age, the range is 1,500-8,500/µL.
An increase in circulating neutrophils is a result of a disturbance of the normal equilibrium involving bone marrow neutrophil production, movement out of the marrow compartments into the circulation, and neutrophil destruction. Neutrophilia may arise either alone or in combination with enhanced mobilization into the circulating pool from either the bone marrow storage compartment or the peripheral blood marginating pool, by impaired neutrophil egress into tissues, or by expansion of the circulating neutrophil pool secondary to increased granulocytopoiesis. Myelocytes are not released to the blood except under extreme circumstances.
Acute Acquired Neutrophilia
Neutrophilia is usually an acquired, secondary finding associated with inflammation, infection, injury, or stress. Acute or chronic bacterial infections, trauma, and surgery are among the most common causes encountered in clinical practice. Neutrophilia may also be associated with heatstroke, burns, diabetic ketoacidosis, or any other acute stress. Drugs commonly associated with neutrophilia include epinephrine, corticosteroids, and recombinant growth factors such as recombinant human granulocyte colony-stimulating factor (rhG-CSF) and recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF).
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