Neutropenia

Neutropenia is a condition characterized by an abnormally low number of neutrophils, a type of white blood cell essential for defense against bacterial and fungal infections. It is typically defined by an absolute neutrophil count (ANC) below 1.5 × 10^9/L. Severity is commonly categorized as mild (ANC 1.0–1.5 × 10^9/L), moderate (0.5–1.0 × 10^9/L), or severe (below 0.5 × 10^9/L). The clinical concern increases with duration and depth of neutropenia, because infection risk grows as neutrophil numbers fall and recover more slowly.

Common causes include cytotoxic chemotherapy and radiation therapy, especially in cancer patients, which suppress bone marrow production. Other drugs (for example clozapine, methotrexate), bone marrow disorders, autoimmune diseases, infections, nutritional deficiencies, and inherited or acquired bone marrow failure can also cause neutropenia. In some cases no clear cause is found.

Many individuals are asymptomatic. When infection occurs, fever may be the presenting sign since neutrophil-mediated inflammation can be blunted. A CBC with differential confirms the low neutrophil count, and repeat counts help distinguish transient from persistent neutropenia. If neutropenia is prolonged or unexplained, further evaluation, including bone marrow examination, may be considered. Evaluation for infection should guide management.

Management focuses on the underlying cause and the risk of infection. In cancer patients, granulocyte colony-stimulating factors (G-CSF) such as filgrastim or pegfilgrastim may shorten neutropenia duration. Febrile neutropenia—a fever in the setting of neutropenia—is a medical emergency requiring prompt hospital assessment and empiric broad-spectrum IV antibiotics. Prophylactic antibiotics or antifungals are used in selected high-risk patients. Good oral hygiene and infection prevention measures are advised; live vaccines are avoided during neutropenia.

Prognosis depends on the cause, depth, and duration of neutropenia, as well as the presence of infections. Prevention strategies include modifying chemotherapy regimens, using growth factors when appropriate, and implementing infection control measures.