Reasoning GP · Algorithm · 1-page summary
Leucopenia (low white cell count)
For: adults with a low WCC or neutrophil count on FBC in primary care. Not for: children (this pathway is adult only). Unwell on anticancer treatment → block 0 and the acute oncology service.
Core rule: the absolute neutrophil count (ANC), its trend and the other cell lines set the urgency, not the total WCC. Any low ANC with fever, sepsis features or deterioration, or anyone unwell on (or within 30 days of) anticancer treatment, goes to hospital now: do not wait for the ANC or cultures.
0Stop — emergency assessment now — fever is not required; it can be absent with neutropenia or steroids
- Shock or rapid deterioration: hypotension, confusion, respiratory compromise → 999; follow the local sepsis pathway and resuscitation guidance while arranging transfer.
- On anticancer treatment now or in the last 30 days with fever, feeling unwell or possible infection, even if temperature <38°C → acute oncology service now + Immediate hospital. Neutropenic sepsis (CG151): ANC ≤0.5 × 10⁹/L with temperature >38°C or sepsis features.
- Any ANC with fever, sepsis features or deterioration (rigors, new cough, breathlessness, dysuria, diarrhoea) → Immediate hospital; do not wait for a repeat FBC, the ANC or cultures.
- Severe mucositis, cannot swallow, drooling (agranulocytosis, aspiration risk) → Immediate hospital
1Triage by ANC — repeat FBC + differential; ANC = WCC × neutrophil %
| ANC (× 10⁹/L) | Action (well, afebrile) |
|---|---|
| <0.5 severe | New, falling or unexplained → Same-day haematology/acute medicine discussion, even afebrile. Systemic symptoms → Immediate hospital. Stable chronic → local policy, not 999. |
| 0.5–1.0 moderate | Persistent → Urgent haematology advice/referral. |
| 1.0–1.5 mild | Stable, isolated, asymptomatic → repeat and investigate selectively. |
| Other lines low | Pancytopenia → Urgent haematology even if stable, mild; red flags → block 2. |
2Screen — serious causes
- Blasts, or a film suggesting acute leukaemia; pancytopenia with bleeding, infection or severe anaemia → Immediate specialist
- New pancytopenia, dysplasia, rapidly falling counts → Same-day haematology
- Petechiae, spontaneous bruising, mucosal bleeding → Same-day haematology
- Clozapine, carbimazole, sulfasalazine, DMARD + sore throat/fever or very low ANC → urgent FBC, Same-day assessment, contact specialist team. Carbimazole: stop now. Clozapine: mental health team pathway; do not stop it alone if stable.
- Neutropenia + spleen, nodes, recurrent infections or constitutional symptoms; abnormal film → Urgent haematology
3Assess
☐ Obs ☐ Mouth: ulcers, mucositis, candida ☐ Nodes, spleen, skin, joints, chest ☐ Full drug review
Tests: repeat FBC + differential; film if persistent, unexplained or other cytopenias; U&E, LFTs; B12/folate and HIV where indicated. Autoimmune tests only with features. No bone marrow or G-CSF in primary care.
4Classify — isolated vs other lines
- Post-viral — mild, isolated → repeat FBC. Drug — temporal link (clozapine, carbimazole, DMARDs, valproate, captopril, beta-lactams).
- Benign ethnic / Duffy-null — well, stable, isolated, normal film, no recurrent infection; never from ethnicity alone. ANC persistently <1.0 or falling → haematology advice.
- Autoimmune — SLE (malar rash, lymphopenia), RA + splenomegaly (Felty) → ANA, RF.
- Marrow or B12/folate — other cytopenias, macrocytosis (MDS, leukaemia, aplasia).
- Lymphopenia (<1 × 10⁹/L) — HIV, steroids, chemotherapy, SLE, sarcoid; if unexplained, offer an HIV test.
- Uncertain — say so; repeat FBC + film, discuss with haematology.
5Treat today — the cause; protect the patient
- Suspected drug: withhold where safe via its own pathway (block 2). B12/folate deficiency: hydroxocobalamin 1 mg IM 3× weekly for 2 weeks, then every 2–3 months (neurological: alternate days until no further improvement); folic acid 5 mg OD, never alone until B12 deficiency excluded or treated. Doses: NICE/SPC, BNF, local formulary.
- Confirmed benign neutropenia: no treatment; reassure, written information.
- Advice: hygiene; flu and pneumococcal vaccines; no live vaccines if immunosuppressed (Green Book). No prophylaxis for a low ANC alone.
6Refer routinely and follow up
- Persistent ANC 1.0–1.5 not explained by benign neutropenia; autoimmune or chronic idiopathic neutropenia → Routine haematology per local guidance.
- Keep in primary care: stable isolated mild, improving post-viral, confirmed benign, mild drug-related improving after specialist advice.
- Re-refer: ANC falling despite stopping the drug, recurrent infections, falling Hb or platelets. HIV with cytopenia, ?TB → infectious diseases.
7Never reassure by
- A normal temperature: neutropenia and steroids blunt fever.
- Few signs or a normal CRP: neutropenic pneumonia and sepsis can look mild.
- A patient on anticancer treatment who “looks well”.
- Each value being “mild” while the ANC falls (1.5 → 1.0 → 0.7).
- Ethnicity alone as proof of benign neutropenia.
- A stable, mild pancytopenia: unexplained still needs urgent haematology.
8Safety-net — say it, then document it
999 / now “Fever, shivering or feeling unwell on cancer treatment, or in the 30 days after it — ring your oncology hotline now. Call 999 if you are confused, breathless, collapsing or getting rapidly worse. Can’t swallow and drooling — go to hospital now.”
Same day “New mouth ulcers, sore throat, pain passing urine, cough with breathlessness, diarrhoea or tummy pain — get seen today; don’t wait for a temperature.” On clozapine, carbimazole or a DMARD: sore throat or fever → urgent same-day blood test.
✓Safe to leave primary care only if — all five, documented
Well and afebrile; no block 0–2 feature
ANC, trend, Hb, platelets and film (if indicated) reviewed
Drug review done; any culprit handled via its pathway
Repeat FBC or referral owner and date set
Infection advice and safety-net given
Summary of the full Reasoning GP leucopenia algorithm, which holds the examination, investigations, prevention advice and evidence. Sources: NICE CG151 Neutropenic sepsis; NICE NG12 Suspected cancer (updated April 2026); UKHSA Green Book; local acute oncology/haematology contact pathway. Clinical reference — check doses: NICE/SPC, BNF.