What is neutropenia?
Neutropenia occurs when the peripheral blood contains an abnormally low number of circulating neutrophils, a type of white blood cell that helps the body fight bacterial infections. Diagnosis is made when a blood test, the absolute neutrophil count (ANC), is less than 1.5 x 109/liters.
Neutrophils are essential to the immune system because they help to destroy bacteria. In homeostasis (physiologic health), the body maintains an equilibrium between neutrophil production and utilization. When this balance is disrupted and more neutrophils are needed than are produced, neutropenia results.
Healthy adults produce about sixty billion neutrophils per day, but only a small percentage is usually expended. Neutrophils, sometimes called granulocytes, are produced in the bone marrow and released through the bloodstream. Neutrophils contain microscopic granules (sacs of enzymes) that help them kill and digest invading microorganisms through a process known as phagocytosis. People with neutropenia cannot rid the body of these foreign organisms and thus become highly susceptible to infection.
SCN is characterized by abnormalities in neutrophil production and classified as congenital, cyclic, and chronic idiopathic neutropenia, the causes of which are thought to be a receptor signaling/postreceptor defect, a regulatory defect, and faulty immune mechanisms, respectively. SCNs affect the body’s integumentary system and cause infections in the oropharyngeal (throat), respiratory, and gastrointestinal mucosa; the hair follicles; and the skin’s glandular structures.
Kostmann’s syndrome is an inherited disorder that causes significant fever and infection at birth and throughout life. Newborns typically have little evidence of mature neutrophil production and extremely low ANCs (0.1 x 109/liters). People with cyclic neutropenia have recurring three-to-six-day episodes of neutropenia followed by recovery, and are especially prone to fever and infection during extreme neutropenic periods when ANCs can fall as low as 0.1 x 109/liters. In chronic idiopathic neutropenia, ANCs are normal at birth but become lower in time, thus predisposing patients to infection.
Autoimmune neutropenia occurs when the immune system attacks the body’s own blood neutrophils; diagnosis requires that neutrophil-specific antibodies be present. Many drugs used to treat autoimmune diseases cause bone marrow suppression, compromising blood cell production and increasing the risk for neutropenia.
Chemotherapy-induced neutropenia (CIN) is a serious side effect of cancer treatment. In chemotherapy, cytotoxic agents destroy bone marrow cells and strip the body of its natural defenses against infection. Patients who become very neutropenic may need to halt chemotherapy or have their dosages lowered to prevent infection. CIN is called febrile neutropenia when fever develops in patients with ANCs below 500/cubic millimeters. Fever is the body’s response to infection and is especially troubling in these patients because they do not show the usual signs of redness, swelling, and pus associated with infection.
Neutropenia, particularly CIN, results in high morbidity and mortality, increases medical costs, and lowers quality of life. The challenge is to minimize the incidence of infection with the judicious use of therapeutic interventions, such as granulocyte colony stimulating factor (G-CSF) or hematopoietic growth factor, corticosteroids, and broad-spectrum antibiotics.
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