Reasoning GP · Algorithm · 1-page summary
Pancytopenia (low Hb, white cells and platelets)
For: adults with all three cell lines low on FBC in primary care. Not for: children (use paediatric pathways). Already under haematology or oncology and unwell → their 24-hour hotline or 999 (block 0).
Core rule: pancytopenia is never benign. Request an urgent blood film for haematologist review, exclude neutropenic sepsis, bleeding and blasts today, and refer haematology in parallel — do not wait for first-line bloods.
0Stop — call 999 now — before any work-up
- Fever or other sepsis features = neutropenic sepsis until proved otherwise, however well the patient looks → 999. IV antibiotics within 1 hour; do not wait for cultures. Known neutropenia + temperature ≥37.5°C → 999 or oncology hotline
- Spontaneous bruising, petechiae, bleeding gums, any active bleeding, or platelets <20 × 10⁹/L → 999 / Same-day haematology. Sudden confusion or focal neurology with low platelets (intracranial bleed) → 999
- While waiting: stop any myelosuppressive culprit drug. Do not delay transfer or referral for B12, folate or other first-line bloods.
1Triage by severity — film + lowest count + symptoms
| Finding | Action |
|---|---|
| Emergency | Blasts on film; ANC ≤0.5 + fever; platelets <20 or bleeding; severe aplastic anaemia → 999 / Same-day haematology |
| Unexplained | No clear cause, dysplasia or unexplained macrocytosis on film, MDS suspected → Urgent haematology (local pathway) |
| Monitor closely | Drug stopped; progressive fall on serial FBCs; splenomegaly without malignancy features → Haematology ≤1 week |
| GP-managed | B12/folate deficiency (MCV up, film without blasts or dysplasia), alcohol, or mild drug-induced with counts recovering → replace, recheck FBC at 6–8 weeks |
2Screen — serious causes
- Blasts on film, rapid onset over days–weeks (acute leukaemia) → Same-day haematology
- Unexplained lymphadenopathy or splenomegaly, especially with night sweats, fever or weight loss → consider a Suspected cancer pathway referral (NG12)
- On methotrexate, carbimazole, clozapine or another myelosuppressive drug → stop it now, urgent FBC. Methotrexate: folinic acid rescue. Carbimazole: Same-day haematology/endocrinology advice; never switch to propylthiouracil. Clozapine: act today via the monitoring service (red → stop).
- Jaundice, hepatomegaly + travel → urgent leishmaniasis serology, tropical medicine referral.
3Assess
☐ Temperature, obs ☐ Pallor, petechiae, bruising, mouth ulcers, gum hypertrophy ☐ Nodes, spleen, liver, jaundice, sternal tenderness ☐ Drugs, alcohol, travel, B symptoms
Tests: FBC, differential, reticulocytes; urgent film for haematologist review (“please review urgently for blasts and dysplasia”); B12, folate, ferritin; LFTs, LDH, urate; TFTs; CRP/ESR; HIV, EBV, CMV, hepatitis B/C; DAT. Low reticulocytes = marrow failure.
4Classify — the mechanism, alongside referral
- Marrow failure — aplastic anaemia (profound, hypocellular); MDS (older, insidious, dysplastic cells).
- Infiltration — leukaemia (blasts), lymphoma, myeloma, myelofibrosis (tear-drop cells), metastatic cancer.
- Megaloblastic — B12 or folate deficiency: raised MCV, hypersegmented neutrophils.
- Drugs — methotrexate, carbimazole, clozapine, carbamazepine, sulfasalazine, chemotherapy.
- Systemic — hypersplenism, viruses (HIV, EBV, CMV, hepatitis, parvovirus), SLE, sepsis, alcohol, leishmaniasis.
- Uncertain — say so; urgent haematology, do not watch and wait.
5Treat today — only once blocks 0–2 are clear
- B12 deficiency confirmed: hydroxocobalamin 1 mg IM 3× weekly for 2 weeks, then every 2–3 months (neurological: alternate days until no further improvement, then every 2 months). Oral cyanocobalamin 50–150 micrograms daily only if diet-related.
- Folate deficiency: folic acid 5 mg OD for 4 months; check B12 first. Doses: NICE/SPC, BNF, local formulary.
- Culprit drug: stop, seek specialist advice. Protect: ANC <1.0 → infection precautions; no live vaccines if immunocompromised; avoid NSAIDs, aspirin, contact sports.
6Follow up and refer
- GP-managed cause: recheck FBC at 6–8 weeks; not improving → refer haematology.
- Shared care: compare each FBC with the last; any downward trend → back to haematology. Fever → hotline, not GP telephone advice alone.
- Reproductive age facing chemotherapy or HSCT → check fertility preservation has been offered before treatment (NG257).
7Never reassure by
- An automated FBC without a film: the analyser misses blasts and dysplasia.
- A well-looking or afebrile patient with a low neutrophil count.
- Pending B12 and folate results: refer in parallel.
- A raised MCV alone: B12/folate must be low and the film free of blasts or dysplasia.
- “Old age” or “iron deficiency” for slow anaemia with infections (MDS).
- Stopping a drug without repeat counts showing recovery.
8Safety-net — say it, then document it
999 / now “Fever, shivering or feeling very unwell — call 999 or go to hospital now; don't wait to see if it settles.” Same day “New bruising, tiny red spots, any bleeding or breathlessness — contact us today; call 999 if bleeding heavily. Avoid ibuprofen, aspirin and contact sports.”
Known neutropenia: own a thermometer, check twice daily; ≥37.5°C → hotline immediately. Cannot contact a patient with a temperature → welfare check.
✓Safe to leave primary care only if — all five, documented
Afebrile, not bleeding; no block 0–2 feature
Film reviewed: no blasts or dysplasia
Cause found, or urgent haematology referral sent
Culprit drug stopped; recheck FBC date set
Safety-net, infection and bleeding advice given
Summary of the full Reasoning GP pancytopenia algorithm, which holds the causes, investigations, specialist treatment, transfusion and shared-care monitoring. Sources: BSH adult aplastic anaemia (2024); NICE NG12 Suspected cancer (updated April 2026); NICE CG151 Neutropenic sepsis; UKONS triage tool; NICE NG257. Clinical reference — follow local haematology pathways and check doses: NICE/SPC, BNF.