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
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 ...