Basophilia Definition
Basophilia is defined as an elevated absolute basophil count in peripheral blood, with hyperbasophilia specifically defined as a persistent basophil count ≥1000 cells/μL, which is highly indicative of an underlying myeloid neoplasm. 1
Quantitative Definition
- Basophilia represents an abnormal increase in basophils, the rarest type of granulocyte in peripheral blood 2
- Hyperbasophilia (≥1000 basophils/μL) serves as a critical diagnostic checkpoint requiring detailed hematologic investigation for myeloid malignancies 1
- In chronic myeloid leukemia (CML), basophilia exceeding 20% in peripheral blood indicates accelerated phase disease according to WHO and European LeukemiaNet criteria 3, 4
Clinical Significance
Basophilia functions as a key diagnostic marker across multiple disease categories:
Myeloproliferative Neoplasms (Primary Association)
- CML typically features basophilia in the initial chronic phase, along with splenomegaly and thrombocytosis per European LeukemiaNet criteria 3, 4
- Testing for Philadelphia chromosome and BCR-ABL rearrangement should be performed to rule out CML when basophilia is identified 4
- Bone marrow biopsies in CML show increased cellularity with myeloid proliferation and commonly demonstrate basophilia at diagnosis 4
- Persistent basophilia in primary myelofibrosis correlates with increased risk of progression to acute myeloid leukemia, particularly in CALR-positive cases 5
Reactive Causes
- Basophils physiologically increase in allergic conditions, chronic inflammation, and parasitic infections 5
- Basophils express high-affinity IgE receptors (FcεRI) and contain histamine granules, making them effector cells in allergic reactions 6
- The basophil activation test (BAT) can aid in diagnosing allergic conditions 3
Pathophysiologic Mechanisms
- Basophils share morphological and functional characteristics with tissue mast cells, including IgE receptor expression and histamine content 6
- In anaphylaxis, basophils alongside mast cells mediate systemic release of inflammatory mediators 3
- Elevated histamine levels from basophilia can cause rare manifestations such as upper gastrointestinal ulceration in CML patients 3, 4
Diagnostic Approach
When basophilia is identified, a systematic evaluation is required:
- First, confirm true basophilia by excluding spurious elevations from technical or analytical errors 7
- Second, evaluate for symptoms suggesting reactive causes (allergies, infections, inflammation) versus clues to neoplastic disease 7
- Third, if myeloid neoplasm is suspected or basophilia persists without reactive cause, proceed with Philadelphia chromosome/BCR-ABL testing and consider bone marrow biopsy 4, 7