Synopsis
Interpret raised white-cell counts by lineage, time course and morphology, recognise reactive physiological and infective patterns, and escalate blasts, clonal lymphocytosis or unexplained persistence appropriately.
- Leucocytosis is a laboratory description; classify the absolute neutrophil, lymphocyte, monocyte, eosinophil and basophil counts rather than interpreting the total alone.
- Neutrophilia commonly accompanies bacterial infection, inflammation, tissue necrosis, corticosteroids, smoking, pregnancy, G-CSF, stress and splenectomy.
- Reactive lymphocytosis is common in viral infection and can show large activated lymphocytes; pertussis and some bacterial or parasitic infections also raise lymphocytes.
- Corticosteroids cause neutrophil demargination with lymphopenia and eosinopenia, often without the left shift or toxic change expected in intense bacterial inflammation.
- A blood film can identify toxic granulation, Döhle bodies, reactive lymphocytes, blasts, dysplasia, smudge artefact and immature myeloid cells and is central to triage.
- Basophilia, persistent myeloid left shift and splenomegaly raise chronic myeloid leukaemia and warrant BCR::ABL1 testing through haematology.
- Persistent clonal-appearing lymphocytosis, lymphadenopathy, splenomegaly, cytopenias or B symptoms prompts flow cytometry and a lymphoproliferative pathway.
- Repeat a clinically plausible reactive count after recovery because trajectory often separates transient response from a persistent clonal process.
- Leukaemoid reactions can reach striking counts in severe infection, inflammation or growth-factor exposure, but magnitude alone cannot reliably distinguish them from myeloid neoplasia.
- Treat the underlying cause rather than the number in uncomplicated reactive leucocytosis; cytoreduction is reserved for specialist malignant or hyperviscosity indications.
Key red flags
New hypoxia, confusion, focal neurology or retinal disturbance with suspected acute leukaemia requires emergency cytoreduction planning.
Investigation priorities
Confirm lineage, persistence and associated cytopenias.
Management branches
A raised white-cell count is accompanied by systemic or haematological symptoms.
- Assess breathing, neurology, retina, bleeding, infection and spleen and review haemoglobin, platelets, film flags, coagulation and tumour-lysis markers.
- Call haematology immediately for blasts, promyelocyte concern, leukostasis physiology, major cytopenias or tumour lysis and avoid delaying definitive sampling.
- Treat sepsis and other physiological emergencies in parallel, recognising that infection and leukaemia can coexist.
Key medicines
No medicine for an uncomplicated reactive countDo not prescribe cytoreduction or antimicrobial treatment solely for the white-cell number; treat a clinically defined infection, inflammation or exposure using its own regimen.A reactive hypothesis requires follow-up to resolution; persistent, basophilic, blast-containing or symptomatic leucocytosis still needs haematology assessment.
Emergency cytoreductionA haematologist selects hydroxycarbamide, leukapheresis or disease-specific induction according to leukaemia subtype, symptoms, count kinetics and tumour-lysis risk.Do not begin empirically without preserving diagnostic samples and specialist direction; anticipate tumour lysis, cytopenias, infection and reproductive implications.