Immunology and AllergyTier 2Disease (DEADMAN)

Neutrophil abnormalities - neutropenia

Description

Reduced circulating neutrophil count (commonly defined as <1.5 x10^9/L, with severe neutropenia <0.5 x10^9/L) - infection risk rises sharply as the count falls, particularly below the severe threshold

Epidemiology

Common causes vary by context: drug-induced (chemotherapy, clozapine, carbimazole, and many others) is the leading cause in adults presenting acutely; viral infection is a common transient cause; congenital/cyclic neutropenia is rare

Aetiopathogenesis

Reduced production (marrow failure, infiltration, chemotherapy, B12/folate deficiency), increased destruction (autoimmune, drug-induced immune-mediated), or redistribution/sequestration (rare)
Febrile neutropenia reflects the combination of infection risk with a blunted inflammatory response - clinical signs of infection (pus, marked localising signs) may be minimal since neutrophils are needed to generate them

Diagnosis

FBC + differential confirms the count and severity; peripheral film for morphology; bone marrow examination if the cause is unclear or a marrow process is suspected
Drug history is essential - neutropenia should be assumed drug-induced until proven otherwise in a patient on a culprit medication, given how common this is

Management

Febrile neutropenia is a medical emergency - empirical broad-spectrum IV antibiotics within 1 hour of presentation, before the causative organism is identified
G-CSF can accelerate neutrophil recovery in selected settings (chemotherapy-induced neutropenia with risk factors)
Stop/switch the causative drug where drug-induced neutropenia is identified

Associations

Chemotherapy, clozapine (mandatory monitoring), carbimazole, viral infection, autoimmune neutropenia, bone marrow failure syndromes

Natural history & complications

Most drug-induced neutropenia recovers within 1-3 weeks of stopping the causative agent; the risk during the neutropenic window (overwhelming bacterial/fungal sepsis) is what drives the emergency management approach, not the neutropenia itself

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