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Neutropenia designates a blood absolute neutrophil count that is less than two standard deviations below the normal population mean. Neutropenia can be inherited or acquired. It usually results from decreased production of neutrophil precursor cells in the marrow. Neutropenia also can result from a shift of neutrophils from the circulating into the marginated cell pools in the circulation. Less commonly, neutropenia results from accelerated destruction of neutrophils or increased egress of neutrophil from the circulation into the tissues. Neutropenia can occur with anemia, thrombocytopenia, or both, in which case the condition is a bicytopenia or pancytopenia. When neutropenia is the sole or dominant abnormality, the condition is called “selective” or isolated” neutropenia, such as chronic idiopathic neutropenia or drug-induced neutropenia. In some diseases, several cell lineages are mildly affected but the reduction in neutrophil is the most severe, such as Felty syndrome. Neutropenia may be an indicator of an underlying systemic disease, such as early vitamin B12 deficiency. Neutropenia, particularly severe neutropenia (counts <500 neutrophils/μL [0.5 × 109/L]), increases susceptibility to bacterial or fungal infections and impairs the resolution of these infections. Therapy with granulocyte colony-stimulating factor is helpful in increasing blood neutrophil counts for many types of neutropenia. Neutrophilia is an increase in the absolute neutrophil count to a concentration greater than two standard deviations above the normal population mean value. Neutrophilia contributes to the inflammatory response and to resolution of infections. Inflammatory and infectious diseases are the most frequent causes of neutrophilia. Bacterial infections usually produce neutrophilia, whereas viral infections may not produce neutrophilia or may raise the neutrophil count only slightly. Solid tumors occasionally engender striking neutrophilia. When the neutrophil count is very high, it may be referred to as a leukemoid reaction. The rare neutrophilic variants of chronic myeloid leukemia and chronic neutrophilic leukemia may result in striking neutrophilia. Demargination of neutrophils or rapid release of neutrophils from a large marrow pool may transiently increase the blood neutrophil count. Sustained increased require increased production of these cells.

Acronyms and Abbreviations

Acronyms and abbreviations that appear in this chapter include: ANA, antinuclear antibody; G-CSF, granulocyte colony-stimulating factor; GM-CSF, granulocyte-macrophage colony-stimulating factor; Ig, immunoglobulin; IL, interleukin; SDF-1, stromal cell-derived factor-1.

Neutropenia refers to an absolute blood neutrophil count (total leukocyte count per microliter × percent of neutrophils) that is less than two standard deviations below the normal mean of the population. The terms leukopenia, a reduced total white blood cell count, and granulocytopenia, reduced numbers of blood granulocytes (neutrophils, eosinophils, and basophils), sometimes are imprecisely used as synonyms for neutropenia. Agranulocytosis literally means a complete absence of blood granulocytes, but this term often is used to indicate severe neutropenia, that is, counts less than 0.5 × 103/μL (0.5 × 109/L).

The concentration of neutrophils in blood is influenced by age, activity, and genetic and environmental factors (see Chap. 2). For children from 1 month to ...

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