Table 9-1 lists the causes of leukocytosis. The normal leukocyte counts and the absolute counts of different classes of leukocytes vary with age in children, and their ranges are listed in Appendix Table A1-15. Leukocytosis may be acute or chronic and may result from an increase in one or more specific classes of leukocytes.

Table 9-2 lists the causes of monocytosis and monocytopenia, Table 9-3 the causes of basophilia, and Table 9-4 the causes of neutrophilia. Eosinophils and lymphocytes are discussed later in this chapter.

For the purposes of quantitative interpretation, it is important to calculate the absolute count of each class of white blood cell (WBC) rather than the relative percentage count. If nucleated red blood cells (nRBCs) are present, the total WBC count includes the total nucleated cell count (TNCC). Under these circumstances the true total WBC count is calculated by subtracting the absolute nRBC count from the TNCC. This correction is generally required in the hemolytic anemias.

Blood smear examination of the white cell morphology is important in the diagnosis of various causes of leukocytosis; for example, in severe infections or other toxic states, the neutrophils may contain fine deeply basophilic granules (toxic granulation) or larger basophilic cytoplasmic masses (Döhle bodies); vacuolization of neutrophils may also occur. Döhle bodies are also found in pregnancy, burns, cancer, May Hegglin anomaly, and many other conditions. Infants and children have a tendency to release immature granulocytes into the circulation, and the WBC count may reach very high levels (>50,000/mm3). This is called a leukemoid reaction. The shift to the left may be so marked as to suggest myeloid leukemia. Table 9-5 lists the distinguishing features of leukemoid reaction and true leukemia.

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