Neutropenia
An abnormally low count of neutrophils (a type of white blood cell), increasing susceptibility to infection. Neutropenia is a feature of Barth syndrome (treated with elamipretide) and can be a side effect of certain medications including some chemotherapy agents.
Technical Context
Neutropenia grading (NCI CTCAE): Grade 1 (ANC 1500-2000/μL), Grade 2 (1000-1500), Grade 3 (500-1000), Grade 4 (<500 — severe, high infection risk). Causes: decreased production (bone marrow failure, chemotherapy, drug-induced), increased destruction (autoimmune, hypersplenism), and increased margination. In Barth syndrome, neutropenia is cyclic or intermittent (caused by mitochondrial dysfunction in neutrophil precursors — elamipretide may improve neutrophil counts by improving mitochondrial function). Chemotherapy-induced neutropenia is the primary clinical context for G-CSF (filgrastim, pegfilgrastim — stimulating neutrophil production). Febrile neutropenia (ANC <500 + fever ≥38.3°C) is a medical emergency requiring immediate empirical broad-spectrum antibiotics — antimicrobial peptide drugs (vancomycin, daptomycin) are used when gram-positive coverage is needed.