What is basophilia?

Basophilia Definition

Basophilia is defined as an increased number of basophils in the peripheral blood, typically considered when the absolute basophil count exceeds 1000 per μL of blood (hyperbasophilia). 1

Normal Basophil Values and Clinical Significance

• Basophils are the rarest type of granulocytes, normally representing approximately 0.01-0.3% of blood leukocytes 2
• Hyperbasophilia (≥1000 basophils/μL) is highly indicative of an underlying myeloid neoplasm and requires detailed hematologic investigation 1
• Basophilia is a key diagnostic feature in several hematologic conditions, particularly myeloproliferative neoplasms 3

Conditions Associated with Basophilia

Neoplastic Causes

• Chronic Myeloid Leukemia (CML): Basophilia is a typical feature of CML in the initial chronic phase, along with splenomegaly and thrombocytosis 3
• Basophilia exceeding 20% in peripheral blood is considered a criterion for accelerated phase in CML 3
• Persistent basophilia in primary myelofibrosis may suggest an "accelerated phase" toward acute myeloid leukemia development 4
• Acute and chronic basophilic leukemias, although rare, have been described 1

Non-Neoplastic (Reactive) Causes

• Allergic disorders: Basophilia often accompanies eosinophilia in allergic conditions 5
• Chronic inflammatory conditions 6
• Parasitic infections 7
• Type 2 immune responses 5

Diagnostic Approach to Basophilia

1. Confirm true basophilia: Rule out spurious basophilia (laboratory error) 7

2. Evaluate for reactive causes:

   • Check for allergic symptoms, chronic inflammation, or parasitic infections 7, 6
   • The basophil activation test (BAT) can be useful in diagnosing allergic conditions 8

3. Screen for myeloid neoplasms:

   • Testing for the Philadelphia chromosome and BCR-ABL rearrangement should be considered to rule out CML 3
   • Bone marrow biopsy may show increased cellularity due to proliferation of myelopoiesis in CML 3

Clinical Implications

• Rare manifestations of CML including upper gastrointestinal ulceration can occur from elevated histamine levels due to basophilia 3
• Basophils can play either beneficial or deleterious roles in inflammation depending on the context 6
• In anaphylaxis, basophils (along with mast cells) are involved in the systemic release of mediators 8

Monitoring and Management

• For persistent unexplained basophilia, regular monitoring of complete blood counts is recommended 7
• In cases of hyperbasophilia without an obvious cause, referral to a hematologist is warranted 1
• When basophilia is identified as part of a myeloid neoplasm, treatment should target the underlying condition 3, 4

Pitfalls in Diagnosis

• The reliability of basophil counts can be insufficient, whether performed by microscopic examination or by hematology analyzers 7
• Basophilia may be overlooked due to the rarity of these cells in normal blood 2
• Basophils should not be confused with mast cells, which are tissue-resident cells with distinct functions 6, 2