Paper I
Question
What are the types of Leukemoid reaction. Discuss the causes.
Answer
A leukemoid reaction is a benign, reactive leucocytosis (typically >50,000/mm³) resembling leukaemia in peripheral blood picture but caused by a non-leukaemic underlying condition, without an underlying malignant clonal proliferation.
Types
- Myeloid (neutrophilic) leukemoid reaction: Marked neutrophilic leucocytosis with left shift (immature granulocyte forms — myelocytes, metamyelocytes, band forms) in peripheral blood, resembling chronic myeloid leukaemia
- Lymphoid leukemoid reaction: Marked lymphocytosis, resembling chronic lymphocytic leukaemia or lymphoma, typically seen with certain infections (e.g., pertussis, infectious mononucleosis)
- Eosinophilic leukemoid reaction: Marked eosinophilia, seen with parasitic infestations, allergic conditions
Causes
- Infections: Severe bacterial infections/sepsis, tuberculosis, pertussis (lymphoid type)
- Severe haemolysis or haemorrhage
- Malignancy (paraneoplastic): Certain solid tumours secreting growth factors (e.g., G-CSF-producing tumours)
- Severe burns, trauma, surgery
- Drug reactions, corticosteroid therapy
- Poisoning (e.g., mercury poisoning)
Distinguishing from true leukaemia
- Leukocyte alkaline phosphatase (LAP) score: elevated in leukemoid reaction, low/absent in CML
- Absence of Philadelphia chromosome/BCR-ABL fusion
- Resolution with treatment of the underlying cause
- Absence of basophilia (typically present in CML)