Screen for acute leukaemia, blast crisis, hyperviscosity syndrome, and sepsis. These require same-day haematology or emergency admission.
Hyperleukocytosis (WCC >100) causes blood hyperviscosity leading to leucostasis in cerebral and pulmonary vessels. Mortality rate 20-40% if untreated within hours. Requires emergency leukapheresis or chemotherapy.
Blast cells indicate acute leukaemia (AML/ALL). Median survival without treatment is weeks to months. Same-day referral enables bone marrow biopsy and rapid chemotherapy initiation.
B symptoms (fever, sweats, weight loss) in the context of leucocytosis suggest haematological malignancy. NICE NG12 mandates 2WW for suspected haematological cancer.
Septic leucocytosis can reach 30-50 × 10⁹/L (leukaemoid reaction). The leucocytosis is secondary; the priority is identifying and treating the source of infection urgently.
Confirm persistent leucocytosis and identify the predominant white cell lineage. A single raised WCC may be transient (infection, stress, exercise).
Transient leucocytosis is common after infection, stress, exercise, or smoking. A single raised WCC does not mandate extensive investigation. Repeating the FBC avoids unnecessary anxiety and costly tests.
The differential is key. Neutrophilia (bacterial infection, CML), lymphocytosis (viral infection, CLL), eosinophilia (allergy, parasites), and monocytosis (chronic infection, CMML) each have distinct causes and management pathways.
Blood film review by a haematologist can detect morphological abnormalities (blasts, smudge cells, left shift) that automated counters miss. It is the single most important diagnostic step after confirming persistent elevation.
Classify leucocytosis by the cell type that is elevated. This determines the differential diagnosis and investigation pathway.
Neutrophilia is the most common leucocytosis pattern (70% of cases). Most are reactive (infection, steroids, smoking). Persistent neutrophilia >20 × 10⁹/L without infection raises concern for CML.
Lymphocytosis in adults with persistent count >5 × 10⁹/L for >3 months is CLL until proven otherwise. Flow cytometry (CD5+/CD19+/CD23+) confirms diagnosis.
Eosinophilia requires travel history (parasites are the leading cause worldwide). Persistent eosinophilia >1.5 × 10⁹/L for >6 months with organ damage defines hypereosinophilic syndrome (requires urgent haematology referral).
Basophilia is rare but highly specific for CML when present. In CML, basophils are often accompanied by the entire spectrum of myeloid maturation on blood film (left shift).
Examine for splenomegaly, hepatomegaly, and lymphadenopathy. These findings narrow the differential and guide referral urgency.
Splenomegaly in leucocytosis is highly significant. Massive splenomegaly (>8 cm below costal margin) suggests CML, myelofibrosis, or hairy cell leukaemia. Moderate splenomegaly occurs in CLL, lymphoma, and infectious mononucleosis.
Lymphadenopathy differentiates malignant from reactive causes. Rubbery, non-tender nodes >2 cm persisting >4 weeks warrant 2WW referral for lymphoma exclusion. Tender, mobile nodes suggest reactive hyperplasia.
Hepatomegaly + splenomegaly together strongly suggest haematological malignancy (CML, CLL, lymphoma) or chronic infection (EBV, CMV). Isolated hepatomegaly is more often due to liver pathology or heart failure.
Investigate based on the predominant cell lineage and clinical context. Avoid shotgun testing; target investigations to the likely differential.
Blood film review is the single highest-yield investigation. It costs £10-20 and can diagnose acute leukaemia, CML, CLL, and infectious mononucleosis. Automated differentials miss 10-15% of abnormalities.
Flow cytometry (immunophenotyping) is diagnostic for CLL (CD5+/CD19+/CD23+). It can be performed on peripheral blood and does not require bone marrow biopsy in most cases. Sensitivity >95%.
LDH elevation (>500 U/L) is non-specific but indicates high cell turnover. Seen in haematological malignancy, haemolysis, and tumour lysis syndrome. Helps triage urgency of haematology referral.
Targeted investigation based on predominant cell type avoids unnecessary tests and anxiety. A patient with isolated neutrophilia does not need parasite serology; a patient with eosinophilia does not need BCR-ABL testing.
Refer based on the degree of elevation, persistence, associated features, and blood film findings.
WCC >50 × 10⁹/L is the threshold for same-day referral even without symptoms. At this level, the risk of leucostasis, tumour lysis syndrome, and undiagnosed acute leukaemia or CML blast crisis is high enough to warrant urgent evaluation.
Persistent lymphocytosis >5 × 10⁹/L in adults is CLL until proven otherwise. NICE NG12 recommends 2WW referral for suspected haematological cancer. Flow cytometry confirms diagnosis in 90% of cases without bone marrow biopsy.
Reactive leucocytosis (infection, steroids, smoking, stress) accounts for 80% of cases in primary care. These do not require haematology referral if the WCC normalizes within 4 weeks of treating the underlying cause.
Blood film abnormalities (blasts, left shift, smudge cells) mandate referral even if WCC is only mildly elevated. Morphology is more important than absolute count in detecting malignancy.
Leucocytosis is a symptom, not a disease. Treatment targets the underlying cause. Primary care can manage reactive causes; haematological malignancy requires specialist input.
Haematological malignancy treatment: Managed by haematology. Primary care role is supportive care, monitoring for complications, and managing treatment side effects.
Reactive leucocytosis resolves when the underlying cause is treated. Antibiotics for infection, steroid taper, smoking cessation, and discontinuing causative drugs are curative. There is no role for treating the WCC itself.
CLL watch-and-wait is evidence-based. Early chemotherapy does not improve survival in asymptomatic CLL. Treatment is reserved for symptomatic disease (bulky nodes, cytopenia, B symptoms). Median survival without treatment is 10+ years in low-risk CLL.
Imatinib for CML has transformed prognosis. 10-year survival is 85-90% with TKI therapy vs 20% with chemotherapy alone. Complete haematological response (WCC <10) is achieved in >95% of patients within 3 months.
Parasite treatment for eosinophilia is empirical if travel history suggests exposure. Stool microscopy has low sensitivity (30-50%) for strongyloides. Albendazole is safe and well-tolerated; treat presumptively in high-risk patients.
Lifestyle interventions reduce cardiovascular and infection risk in patients with chronic leucocytosis, particularly those with haematological malignancy.
Smoking cessation normalizes WCC in 3-6 months and reduces cardiovascular events by 30-40% within 1 year. Smoking doubles the risk of transformation of CLL to aggressive lymphoma (Richter's transformation).
Infection prevention is critical in CLL and other lymphoproliferative disorders. Hypogammaglobulinemia occurs in 50% of CLL patients, increasing pneumonia risk 5-fold. Flu and pneumococcal vaccines reduce hospitalization by 40-50%.
Thrombosis risk in myeloproliferative disorders (ET, PV) is 10-20% over 10 years. Aspirin 75 mg daily reduces arterial thrombosis by 60%. Hydroxyurea or cytoreductive therapy is added if high-risk (age >60, prior thrombosis).
Exercise improves quality of life and reduces fatigue in haematological malignancy. A Cochrane review (2019) showed moderate exercise reduces cancer-related fatigue by 30% (effect size 0.3). Avoid exercise if platelet count <50 × 10⁹/L (bleeding risk).
Monitor WCC trajectory, watch for red-flag symptoms, and re-refer if malignancy suspected. Patients with persistent leucocytosis require long-term surveillance.
WCC trajectory is more important than absolute value. A rising WCC (e.g., 12 → 15 → 20 over 3 months) suggests malignancy or evolving myeloproliferative disorder even if each individual value is not alarm-level.
CLL progression occurs in 1-2% per year. Criteria for starting treatment (Rai staging progression): doubling time <6 months, new cytopenia, progressive lymphadenopathy, or B symptoms. Primary care monitoring detects these early.
Hyperviscosity symptoms (headache, visual changes, confusion) are medical emergencies. At WCC >100, blood viscosity increases 3-5×, reducing cerebral perfusion. Mortality is 20-40% without emergency leukapheresis or chemotherapy within 24 hours.
Patient anxiety about leucocytosis is common. Clear explanation, regular monitoring, and low threshold for haematology referral reduces distress. Many patients fear cancer; early specialist reassurance (even if benign) improves quality of life.