White Cell Count

WCC Result

(Reference range: 2.9-9.6 ×10⁹/L)

 

What is Leucopenia?

Leucopenia refers to a total white cell count (WCC) < 4.0 ×10⁹/L. It reflects reduced immune capacity and may indicate infection, bone marrow failure, autoimmune disease, or medication effects.

Common Causes

  • Viral infections (e.g. influenza, HIV)
  • Bone marrow suppression (e.g. chemotherapy, radiotherapy)
  • Autoimmune diseases (e.g. SLE)
  • Medications (e.g. carbimazole, methotrexate, clozapine)
  • Haematological malignancies (e.g. leukaemia, lymphoma)
  • Sepsis or overwhelming bacterial infections

Stepwise Clinical Approach

Step 1: Confirm and Repeat

Confirm leucopenia is persistent and not due to laboratory error or sampling issues.

If mild and asymptomatic, repeat FBC in 1-2 weeks.

Also request:

  • Blood film: to assess cell morphology, blasts, or abnormal cells
  • CRP and ESR: to assess for infection or inflammatory activity
  • HIV test: to rule out undiagnosed HIV infection
  • ANA and ENA panel: to screen for autoimmune diseases like SLE
  • Vitamin B12 and folate: to check for deficiency-related marrow suppression
  • Liver and renal function tests: to check for systemic disease

These tests help differentiate between benign, infectious, autoimmune, and malignant causes.

Step 2: Identify Red Flags

  • WCC < 2.0 ×10⁹/L
  • Associated anaemia or thrombocytopenia
  • Unexplained infections or fevers
  • Weight loss or lymphadenopathy
  • Abnormal cells on blood film

Urgent referral to haematology is indicated if red flags are present.

Step 3: Review Medications and History

  • Recent viral illness or vaccination?
  • Current or recent use of immunosuppressive or cytotoxic drugs?
  • History of autoimmune disease, HIV, or cancer?

Many mild cases are transient post-viral or drug-related.

Step 4: Interpret Repeat Results

  • If WCC recovers: likely reactive and no further action needed
  • If persistent or worsening: escalate to specialist review

Step 5: Monitor or Refer

  • If mild and stable (3.0-4.0 ×10⁹/L): monitor 3-6 monthly
  • If persistent < 3.0 ×10⁹/L or symptomatic: refer to haematology
 

What is Leucocytosis?

Leucocytosis refers to a total white cell count (WCC) > 11.0 ×10⁹/L. It is often reactive to infection, inflammation, or stress, but persistent high counts may indicate serious pathology such as haematological malignancy.

Common Causes

  • Bacterial infections (especially acute or severe)
  • Inflammation (e.g. trauma, surgery, burns)
  • Medications (e.g. corticosteroids)
  • Smoking
  • Stress response (e.g. seizures, haemorrhage)
  • Haematological malignancies (e.g. chronic myeloid leukaemia)

Stepwise Clinical Approach

Step 1: Confirm and Repeat

Confirm true leucocytosis, not due to haemoconcentration or lab error.

If mild and asymptomatic, repeat FBC in 2-4 weeks.

Also request:

  • CRP and ESR: to assess for ongoing infection or inflammation
  • Blood film: to assess for abnormal cells, blasts, or immature forms
  • Liver and renal function tests: to identify systemic illness
  • Urate and LDH: to screen for rapid cell turnover (may be raised in haematological malignancy)

These tests help distinguish reactive leucocytosis from early myeloproliferative disease.

Step 2: Identify Reactive Causes

  • Recent or ongoing infection?
  • Evidence of inflammation, trauma, or steroid use?
  • Smoking history?

If reactive cause suspected, repeat bloods after clinical recovery or steroid taper.

Step 3: Interpret Repeat Results

  • If WCC normalises: reactive cause confirmed
  • If persistent elevation: proceed to specialist investigations

Step 4: Monitor or Refer

  • If WCC 11–20 ×10⁹/L and improving: monitor clinically and repeat in 1–2 months
  • If WCC persistently > 20 ×10⁹/L or concerning blood film: refer to haematology

Step 5: Red Flags Requiring Urgent Action

  • Presence of blasts, promyelocytes, or atypical cells
  • WCC > 50 ×10⁹/L unexplained
  • Splenomegaly or lymphadenopathy
  • Associated anaemia or thrombocytopenia

Urgent referral to haematology is indicated if red flags are present.

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