What is Basophilia?

Basophilia refers to an elevated basophil count > 0.1 ×10⁹/L. It is rare and often associated with myeloproliferative disorders but may also occur with allergic reactions and chronic inflammation.

Common Causes

Chronic myeloid leukaemia (CML)
Other myeloproliferative neoplasms (e.g. polycythaemia vera, primary myelofibrosis)
Allergic or hypersensitivity reactions
Chronic inflammation (e.g. rheumatoid arthritis, ulcerative colitis)
Infections (rare, e.g. tuberculosis, varicella)

Stepwise Clinical Approach

Step 1: Confirm and Repeat

Confirm basophilia is persistent over repeat samples and not due to laboratory artefact.

When repeating, also request:

Blood film: to assess for blasts or dysplastic cells
Full myeloproliferative screen (JAK2, BCR-ABL): to screen for CML or other MPNs
CRP and ESR: to assess for chronic inflammatory disease
Renal and liver function tests: to exclude systemic illness

These tests help differentiate reactive basophilia from a primary haematological malignancy.

Step 2: Identify Potential Reactive Causes

Recent allergic reactions?
Evidence of chronic inflammation or autoimmune disease?
Recent or ongoing infections?

If a reactive cause is found, manage the underlying condition and monitor basophil levels.

Step 3: Interpretation Based on Results

Normal blood film and mild basophilia: likely reactive
Abnormal blood film or raised WCC: consider myeloproliferative disease
Positive BCR-ABL mutation: diagnostic of chronic myeloid leukaemia (CML)

Step 4: Monitor or Refer

Reactive cause identified: treat underlying cause and monitor FBC every 3-6 months
Persistent unexplained basophilia or concerning features: refer to haematology

Step 5: Red Flags Requiring Urgent Action

Basophilia with marked leucocytosis (high WCC)
Presence of blasts or abnormal cells on blood film
Splenomegaly
Constitutional symptoms (e.g. night fevers, weight loss)

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