Neutropenic sepsis is a medical emergency. Separate four situations: chemotherapy-related febrile neutropenia, chronic isolated neutropenia, drug-induced agranulocytosis, and pancytopenia/suspected marrow failure — they do not share the same thresholds. Follow the local acute oncology/haematology contact pathway.
Neutropenic sepsis (neutrophils ≤0.5 × 10⁹/L with a temperature >38°C or other sepsis features) is a medical emergency. Without neutrophils, infections can progress rapidly to septic shock; risk varies with cause, duration and nadir, mucosal injury, chemotherapy, comorbidity, age and steroid use, so no single mortality figure applies. NICE CG151 requires immediate referral to secondary/tertiary care, where empirical antibiotics are given immediately; treatment should not be delayed for community investigations.
Pancytopenia suggests bone marrow failure (aplastic anaemia, MDS, acute leukaemia). Urgent haematology assessment enables bone marrow examination and supportive care. NICE NG12 (updated April 2026) advises considering a very urgent FBC (within 48 hours) when leukaemia is possible in adults (pallor, persistent fatigue, unexplained fever, persistent or recurrent infection, generalised lymphadenopathy, unexplained bruising, bleeding, petechiae or hepatosplenomegaly), and immediate specialist assessment if a blood count or film suggests acute leukaemia.
Drug-induced agranulocytosis is a recognised risk with clozapine, carbimazole and sulfasalazine. Management is drug-specific: clozapine follows the mandatory monitoring and emergency pathway via the clozapine/psychiatric team; carbimazole requires immediate discontinuation and urgent FBC/medical assessment; DMARDs are withheld and the initiating specialist/shared-care team contacted.
Chemotherapy-induced neutropenia: a patient on anticancer treatment who becomes unwell with fever or other possible infection symptoms needs immediate acute oncology contact and hospital assessment, even if they look well. Neutropenic sepsis is diagnosed in hospital using the clinical context, sepsis features, temperature and ANC; do not delay transfer while awaiting the ANC or cultures.
A low WCC should be interpreted using the local laboratory reference range and the differential count. The clinically important parameter for infection risk is the ANC. Assess whether the abnormality is isolated, persistent, falling, associated with other cytopenias or accompanied by infection/systemic symptoms. A single low WCC can be a lab error or transient viral infection.
Transient leucopenia is common after viral infections (influenza, EBV, CMV). The count usually recovers as the infection settles. Repeating FBC avoids unnecessary investigations and anxiety.
Absolute neutrophil count is the key number. A patient with WCC 3.5, neutrophils 40% (ANC 1.4) has mild neutropenia with low infection risk. A patient with WCC 3.5, neutrophils 20% (ANC 0.7) has moderate neutropenia requiring investigation.
Benign ethnic / Duffy-null-associated neutropenia is a normal variant, not a disease. Some individuals have an ANC below 1.0 × 10⁹/L while remaining well; the diagnosis depends on long-term stability, no recurrent or severe infection, no other cytopenias, a normal blood film and no concerning symptoms or signs — not on ethnicity alone.
Blood film review can detect myelodysplasia (dysplastic neutrophils, hyposegmented nuclei) and early leukaemia (blasts). Automated counters can miss morphological abnormalities.
Classify by severity of neutropenia and whether other cell lines are affected. This determines infection risk and urgency of referral.
Infection risk rises as the ANC falls, but also depends on cause, duration and nadir, mucosal barrier injury, chemotherapy, comorbidity, malignancy, age, corticosteroid treatment, previous infections and local microbiology. A stable chronic ANC of 0.8–1.0 in a well patient is not equivalent to a new falling ANC of 0.8 with fever, mucositis or pancytopenia.
Isolated neutropenia is more likely to be benign (BEN, autoimmune) than pancytopenia. If Hb and platelets are normal, the bone marrow is functioning. Pancytopenia suggests marrow failure or infiltration and requires urgent haematology assessment.
Lymphopenia is less clinically important than neutropenia. Lymphocytes <0.5 × 10⁹/L suggests immunodeficiency (HIV, chemotherapy, immunosuppressants). Offer an HIV test if it is unexplained (an HIV indicator condition), not only when risk factors are present.
Benign ethnic / Duffy-null-associated neutropenia is stable over time. If the ANC is falling, persistently below 1.0, associated with other abnormalities or recurrent infection, seek haematology advice.
Examine for active infection, organomegaly, and signs of underlying systemic disease causing neutropenia.
Oral ulcers and gingivitis are hallmarks of severe neutropenia. Without neutrophils, the mouth cannot mount an inflammatory response to oral bacteria. Severe mucositis with ANC <0.5 increases aspiration pneumonia risk.
Splenomegaly in neutropenia suggests Felty syndrome (RA + splenomegaly + neutropenia). It usually occurs in long-standing RA. The spleen sequesters neutrophils, worsening neutropenia; management is specialist-led.
Malar rash + lymphopenia + neutropenia suggests SLE. Leucopenia is common in SLE. Autoimmune tests are indicated when symptoms or signs suggest SLE, RA, vasculitis or another autoimmune disease.
Absent infection signs in neutropenic patient does not exclude serious infection. Neutrophils are required for pus formation, fever, and inflammatory markers. CRP can be normal despite pneumonia or sepsis. Low threshold for imaging and empirical antibiotics.
Investigate based on the pattern of cytopenia, severity of neutropenia, and clinical context. Target investigations to the likely differential.
B12/folate deficiency is a reversible cause of pancytopenia. Megaloblastic anaemia suppresses all cell lines due to ineffective haematopoiesis. Interpret B12 and folate results against the local laboratory range; replacement reverses the cytopenia.
Drug-induced neutropenia is a common, often immune-mediated cause. Clozapine requires mandatory FBC monitoring under its own monitoring and emergency pathway; patients on carbimazole should have been counselled to stop it and get an urgent blood test if sore throat or fever develops.
HIV testing should be offered in unexplained leucopenia/lymphopenia when clinically appropriate. HIV can cause lymphopenia and neutropenia.
Autoimmune neutropenia (SLE, RA, Felty syndrome) is suggested by positive ANA (SLE), RF (RA), or anti-neutrophil antibodies. Immunosuppressive treatment is specialist-led.
Use a risk-stratified approach based on the ANC, trend, other cytopenias, symptoms, anticancer treatment and local haematology/acute oncology policy (local contact pathway).
New or unexplained ANC <0.5 × 10⁹/L needs urgent same-day discussion even without fever, but the route depends on whether the patient is on chemotherapy, whether the result is new or established and stable, the trend, symptoms, film, comorbidity and local haematology policy. G-CSF is a specialist-led treatment.
Pancytopenia requires urgent bone marrow biopsy to differentiate aplastic anaemia (empty marrow), MDS (dysplastic marrow), and acute leukaemia (blast infiltration). Treatment of aplastic anaemia (immunosuppression or bone marrow transplant) is specialist-led.
Benign ethnic / Duffy-null-associated neutropenia does not require haematology referral once confirmed as stable and isolated with a normal film and no recurrent infection. Reassure the patient this is a normal variant. Routine annual FBC is not necessarily required; follow local haematology advice.
Drug-induced agranulocytosis requires the suspected drug to be withheld and urgent same-day assessment. Any G-CSF is specialist-led. Clozapine rechallenge decisions belong to the clozapine/psychiatric team and monitoring service.
Treatment targets the underlying cause. Primary care can manage benign causes; prophylaxis, G-CSF and immunosuppression are specialist-led.
Prophylaxis and specialist treatments: do not initiate antibiotic or antifungal prophylaxis solely because ANC is below 1.0 or 0.5 × 10⁹/L.
Next steps: see Suspected neutropenic sepsis · Haematological cancers · HIV
Withholding the causative drug is the key step in drug-induced neutropenia, following the drug-specific pathway. Clozapine rechallenge after agranulocytosis is a specialist decision.
G-CSF (filgrastim) stimulates neutrophil production; dose and indication depend on the underlying disorder, body size, renal function, malignancy, chemotherapy protocol and response, so it is specialist-led.
Co-trimoxazole prophylaxis prevents Pneumocystis jirovecii pneumonia (PJP) in selected risk groups. PJP risk relates to CD4 lymphopenia, prolonged high-dose steroids and specific chemotherapy regimens rather than to the neutrophil count alone; prophylaxis is specialist-directed.
Empirical antibiotics in neutropenic fever save lives and should not be delayed for culture results. NICE recommends piperacillin–tazobactam as initial empirical monotherapy for suspected neutropenic sepsis needing IV treatment unless patient-specific or local microbiological factors contraindicate it — this is a secondary-care protocol, not a GP prescription.
Give proportionate advice: hand hygiene, prompt attention to fever or infection symptoms, safe food handling and routine oral/dental care. For most patients with stable isolated mild neutropenia or benign ethnic neutropenia, normal social contact and a normal diet are appropriate. Additional restrictions (prolonged profound neutropenia, stem-cell transplantation, intensive chemotherapy) should be individualised and follow the specialist oncology/haematology plan.
Hand hygiene reduces infection transmission and is the core proportionate precaution.
Food hygiene prevents gastrointestinal infections (Salmonella, Campylobacter, Listeria). Ordinary safe food handling is sufficient for most patients; restrictive diets are reserved for specialist-defined high-risk periods.
Live vaccines (MMR, yellow fever, BCG) contain attenuated virus/bacteria. In immunosuppressed patients, live vaccines can cause disseminated infection; the decision depends on the immunosuppression or treatment, per the Green Book. Inactivated vaccines (flu, pneumococcal) are safe and recommended.
Early recognition of infection is life-saving. Neutropenic patients cannot mount typical signs (pus, high WCC, high CRP). Fever may be the only sign of serious infection — and may be absent in neutropenic or steroid-treated patients. Educate patients to seek help immediately for fever or feeling unwell.
Monitor neutrophil trajectory, watch for infection, and re-refer if ANC falling or recurrent infections. Surveillance intensity depends on the cause, trend and local haematology advice.
ANC trajectory is more important than absolute value. A falling ANC (1.5 → 1.0 → 0.7 over 3 months) suggests evolving bone marrow failure or worsening autoimmune disease, even if each value is "mild." Rising ANC indicates recovery or response to treatment.
Benign ethnic / Duffy-null-associated neutropenia is stable over years without treatment. If ANC is falling, persistently <1.0 or associated with other abnormalities, seek haematology advice to investigate other causes (autoimmune, bone marrow failure). Follow local haematology advice on monitoring.
Neutropenic fever is a medical emergency regardless of how well the patient looks. NICE CG151 requires immediate referral to secondary care and immediate empirical antibiotics in hospital; do not delay transfer for community tests.
Recurrent infections in a neutropenic patient — judged by severity, site, unusual organisms and need for hospital treatment — warrant haematology review. May indicate inadequate neutrophil function despite acceptable count, or progression of underlying disease. G-CSF prophylaxis or immunoglobulin replacement may be needed.