Neutropenia and Neutropenic Sepsis

Introduction

Neutrophils are the principal cellular defence against bacterial and fungal infection. Neutropenia - a reduced absolute neutrophil count - removes this defence, and its most feared consequence, neutropenic sepsis, is one of the true same-day emergencies in medicine: an infection that can progress from mild symptoms to septic shock and death within hours in a patient with no functioning neutrophils to contain it.¹

This topic is approached in two parts: understanding the causes and assessment of neutropenia itself, and recognising and immediately treating neutropenic sepsis when it occurs.

Definitions and grading

Causes of neutropenia

• Cytotoxic chemotherapy - by far the commonest cause encountered in practice, with the neutrophil nadir typically occurring 7-14 days after a cycle, and recovery expected by around day 21
• Drug-induced (non-chemotherapy) - clozapine (mandates regular FBC monitoring), carbimazole, sulfasalazine, and various antibiotics
• Viral infection - a common and usually self-limiting cause, including influenza, EBV, hepatitis and HIV
• Bone marrow failure or infiltration - aplastic anaemia, leukaemia, myelodysplastic syndrome, marrow metastases
• Autoimmune neutropenia, including as part of Felty syndrome (rheumatoid arthritis, splenomegaly and neutropenia) or SLE
• Severe sepsis itself - consumption of neutrophils can occur in overwhelming infection
• Congenital neutropenias (e.g. cyclic neutropenia, Kostmann syndrome) - rare, presenting in childhood with recurrent infection
• Hypersplenism - sequestration alongside other cytopenias
• Severe B12/folate deficiency - as part of a broader pancytopenia

Neutropenic sepsis: definition and recognition

Neutropenic sepsis is defined as a neutrophil count of 0.5 x10^9/L or below (or expected to fall to this level) in a patient with a temperature above 38°C, or with other signs or symptoms consistent with clinically significant sepsis, even without a confirmed fever.²

A source of infection is identified in only around a third of episodes; in the remainder, no organism or focus is ever found, but the risk and the management remain the same.

Assessment and investigations

Investigation must run in parallel with treatment, never delaying it:

• FBC to confirm the neutrophil count
• Blood cultures - peripheral and from any indwelling central line, taken before antibiotics wherever this does not delay treatment
• U&Es, LFTs, CRP, lactate - to assess severity and organ function
• Focused septic screen guided by symptoms - urine culture, chest X-ray, wound/line site swabs, stool culture if diarrhoea
• Do not wait for any of these results before giving antibiotics

Management

Immediate treatment

• Empirical broad-spectrum IV antibiotics within 1 hour of presentation - typically piperacillin-tazobactam monotherapy per local policy, chosen for reliable cover of Gram-negative organisms including Pseudomonas aeruginosa, which cause disproportionately rapid deterioration in this group²
• Sepsis six-equivalent approach - oxygen if hypoxic, IV fluids, blood cultures, lactate, urine output monitoring, alongside the antibiotics
• Escalate to critical care early if there are signs of shock or organ dysfunction
• Adjust or add antibiotic cover based on clinical response, culture results and any localising source, in discussion with microbiology and haematology/oncology

Risk stratification and ongoing care

• The MASCC (Multinational Association for Supportive Care in Cancer) score identifies lower-risk patients (good performance status, no significant comorbidity, outpatient onset) who may be suitable for early switch to oral antibiotics or outpatient management after a period of initial IV treatment and specialist assessment - higher-risk patients require ongoing inpatient IV therapy
• Isolation/protective precautions as per local infection control policy
• G-CSF may be used therapeutically in selected severe or prolonged neutropenia, though its routine use in established neutropenic sepsis (rather than as prophylaxis) is guided by specialist advice rather than automatic
• Review and de-escalate antibiotics once cultures and clinical course allow, balancing infection control against antimicrobial stewardship

Prevention

Primary G-CSF prophylaxis is used with chemotherapy regimens known to carry a high risk of neutropenic sepsis, reducing both the incidence and duration of severe neutropenia. Patients receiving chemotherapy are given clear safety-netting advice (a 24-hour oncology contact number, and instructions to seek urgent assessment for any fever) as standard practice.

Complications

• Septic shock and multi-organ failure - the major cause of mortality if treatment is delayed
• Fungal infection (e.g. invasive aspergillosis, candidiasis) with prolonged or profound neutropenia, particularly beyond 7-10 days
• Delay or dose reduction of subsequent chemotherapy cycles, affecting cancer treatment outcomes
• Death - neutropenic sepsis carries a mortality of several percent even with prompt, appropriate treatment, and substantially higher with delayed treatment

Red flags

Prognosis

With prompt recognition and antibiotics within the recommended timeframe, the large majority of patients with neutropenic sepsis recover fully, particularly if they fall into a lower MASCC risk category.² Outcomes are strongly time-dependent: delayed antibiotic administration is one of the most consistent predictors of mortality in this condition, which is why the 1-hour target is treated as an inviolable standard rather than a guideline to be interpreted loosely.

Neutropenia itself resolves as the underlying cause improves - the marrow recovers after a chemotherapy nadir, an implicated drug is stopped, or the underlying disease is treated - and most patients return to a normal neutrophil count between cycles or after the causative agent is withdrawn.