Reasoning GP · Algorithm · 1-page summary
Eosinophilia
For: a raised eosinophil count on FBC (mild 0.5–1.5, moderate 1.5–5.0, high >5.0 × 10⁹/L) in primary care. Not for: established EGPA or HES on treatment, or DRESS once admitted (follow the specialist plan).
Core rule: organ damage, not the count, sets the urgency. Eosinophilia with cardiac, neurological, respiratory or systemic involvement needs same-day assessment whatever the count, without waiting for duration criteria.
0Stop — call 999 now — any count
- Eosinophilia with haemodynamic instability, severe chest pain, syncope, acute heart failure or respiratory compromise → 999
- Organ involvement but stable (heart, nerves, lungs, DRESS, Strongyloides sepsis) → Same-day hospital; 999 if it becomes unstable.
- Suspected DRESS: stop the suspected culprit drug now. Do not wait for a 4-week or 6-month duration threshold, or for outpatient ANCA.
1Triage by count — descriptive only; organs decide
| Count (× 10⁹/L) | Action |
|---|---|
| Any + organ features | Block 0 / 2 → Same-day hospital |
| 0.5–1.5, well | Repeat FBC + film; single mild rise, clear atopy, normal examination → primary care review. |
| ≥1.5 persistent, unexplained | Initial tests (block 3) → Urgent haematology advice |
| Marked or rising | Urgent haematology advice; ECG, troponin, echo. |
2Screen — one row is enough
- Heart: chest pain, dyspnoea, palpitations, syncope, heart failure, thromboembolism → Same-day hospital ECG, troponin, echo.
- Nerves or lungs: new neuropathy, mononeuritis multiplex, focal deficit, confusion, seizures; hypoxia, haemoptysis, infiltrates → Same-day hospital
- DRESS: new drug (often 2–8 weeks) + rash + fever, ± facial oedema or organ involvement → stop culprit, Same-day hospital
- Strongyloides risk, immunosuppressed, septic → Same-day hospital + urgent ID / tropical medicine.
- EGPA: asthma + sinusitis or polyps + neuropathy or purpura → ANCA, CXR, urinalysis; Same-week rheumatology. ANCA positivity not required.
- Weight loss, fever, night sweats, lymphadenopathy → Urgent haematology advice; consider suspected cancer pathway if unexplained nodes or spleen (NG12).
3Assess
☐ Travel, migration, soil or freshwater exposure ☐ Atopy ☐ Drugs incl. OTC and herbal; any started within 8 weeks ☐ Previous FBCs ☐ Nodes, spleen, rash, chest, heart, neurology
Persistent, ≥1.5 or systemic: repeat FBC + film, U&E/eGFR, LFTs, bone profile, LDH, ESR/CRP, B12. Targeted: Strongyloides IgG if exposed; Toxocara ELISA if dog contact; ANCA only if EGPA suspected; CXR.
Not in primary care: bone marrow and molecular tests (haematology-led).
4Classify — only if the screen is negative
- Atopic (commonest) — mild, well, normal examination → optimise asthma, eczema, rhinitis.
- Drug — NSAIDs, antibiotics, antiepileptics, allopurinol, ACE inhibitors → stop if clinically safe, recheck FBC.
- Parasitic — travel or migration, no atopy → Strongyloides serology; stool tests via microbiology / tropical medicine.
- Haematological (HES, leukaemia, lymphoma) — persistent ≥1.5, abnormal film, cytopenias, splenomegaly → urgent haematology.
- Uncertain — say so. Persists or rises despite treating the cause → look again for drug, parasite, EGPA, haematological cause.
5Treat today — only these
- Atopy: antihistamine (loratadine or cetirizine 10 mg once daily), ICS for asthma, intranasal steroid for rhinitis. Doses: NICE/SPC, BNF, local formulary.
- Suspected drug: stop if clinically safe and document the reaction; specialist advice if the drug is essential. Never rechallenge after DRESS, SJS/TEN, hepatitis or nephritis.
- Strongyloides: ivermectin regimen per tropical medicine / local protocol; immunosuppressed → discuss urgently with ID.
- EGPA, HES, DRESS: treatment is specialist-led; steroids only after discussion unless delay would be dangerous.
6Refer routinely and follow up
- Parasite risk or confirmed helminth → ID / tropical medicine.
- After parasite treatment: FBC at 3 months; still raised → ID / tropical medicine review.
- Recheck FBC after each intervention, timed by count, persistence and symptoms; no routine annual FBC for mild atopic eosinophilia.
- Not responding at review, or new fever or weight loss → GP same week
7Never reassure by
- A "mild" count: 2.0 with organ involvement beats a well 8.0.
- Good asthma or eczema control ("just allergy").
- A negative ANCA: many with EGPA are ANCA-negative.
- Negative stool microscopy: sensitivity is limited.
- Travel long ago: Strongyloides persists for decades.
- Steroids or immunosuppression started without Strongyloides serology if exposed.
8Safety-net — say it, then document it
999 “Call 999 for severe chest pain, fainting, or sudden severe breathlessness.” Same day “New chest pain, palpitations or breathlessness, numbness or weakness, confusion or a fit, coughing blood, or a rash with fever after a new medicine — get seen today.”
Same week “Fever, weight loss or night sweats, or no improvement after treatment — book to see us this week.”
✓Safe to leave primary care only if — all five, documented
No block 0–2 feature; examination normal
Count confirmed on repeat FBC + film; past counts reviewed
Drug, travel and atopy history recorded
Strongyloides serology before any immunosuppression if exposed
Recheck date set; safety-net given
Summary of the full Reasoning GP eosinophilia algorithm, which holds the causes, investigations and evidence. Sources: BSH eosinophilia guideline (2017); BIA returning travellers and migrants (2024); UKHSA migrant health guide; MHRA DRESS and HLA guidance; NICE NG12 (updated April 2026), TA845. Clinical reference — antiparasitic regimens per tropical medicine; check doses: NICE/SPC, BNF.